Hi Jy, welcome to RME user forum.

I could imagine that in certain situations it could be an advantage to have a MIDI port directly on the recording interface.

Some people prefer RME PCI/PCIe-based cards for time-critical instruments like electronic drums.

RME drivers have a high-quality and low latency.

I see here several options.

1. I think the best choice would be the HDSPe AIO Pro €729
https://www.rme-audio.de/de_hdspe-aio-pro.html

- 30 channel I/O
- Balanced (*) stereo analog in- and output, 24-bit/192kHz
- AD/DA converter with only 5/6.25ms samples latency at single speed
- 1x ADAT digital I/O, supporting 192 kHz via S/MUX4 operation
- 1x SPDIF digital I/O, 192 kHz-capable
- 1x AES/EBU digital I/O, 192 kHz-capable
- 1x High-Power Headphone Output, separate DA-converter and playback device (two output levels, high/low power)
- 1x MIDI I/O Hi-Speed Low-Jitter MIDI
- Outputs with Mute relays
- +24 dBu I/O Levels
- SteadyClock FS
- breakout cables: HDSPe AIO Pro: Analog breakout cable, unbalanced (BO9632CMKHPro)
- optional: Word clock module, TCO module (both connected through internal ribbon cable)
- optional breakout cables:
  -  HDSPe AIO/AIO Pro: Analog breakout cable, balanced (BO9632XLRMKH)
  -  HDSPe AIO/AIO Pro: Digital breakout cable, AES/EBU & SPDIF (BO968)

(*) The HDSPe AIO Pro ships in a basic version with analog RCA/phono breakout cables (headphone: TRS jack). Therefore all analog I/Os are unbalanced. An analog XLR breakout cable is available as option (headphone: Neutrik TRS locking jack), turning analog into balanced mode.

PCIe based and ASIO buffer sizes down to 32 samples at single speed.

Based on the reference processors AK5572 and AK4490 derived from the high-end AD/DA converter ADI-2 Pro.
Analog inputs: uses the circuit design of the ADI-2 Pro (+24 / +19 / +13 / +4 dBu).
Analog outputs: reference levels (balanced: +24 / +19 / +13 / +4 dBu; unbalanced: +19 / +13 / +4 / -2 dBu)
Features a dedicated attenuator in the output section, resulting in an increased signal-to-noise ratio and a lower output impedance at low reference levels.
Newly developed, powerful and extremely transparent headphone output.
Thanks to mute relay including switchable output levels, there is no unwanted crackling noise at the headphone output and the analog XLR and RCA outputs when switching on the computer.

2. HDSPe AIO, one of the older PCIe cards, from used market (IMHO, the AIO Pro is superior)
- 1 x Stereo Analog I/O (192 kHz)
- 1 x ADAT I/O (up to 192 kHz via S/MUX4)
- 1 x SPDIF I/O (192 kHz)
- 1 x AES/EBU I/O (192 kHz)
- 1 x MIDI I/O
- 1 x Phones Output (separate DAC, 192 kHz)

PCIe based and ASIO buffer sizes down to 32 samples at single speed.

3. If you need a more portable and USB based version with fast converters, then get the Babyface Pro FS, €809
https://www.rme-audio.de/de_babyface-pro-fs.html
- 12 Input and 12 Output channels
- 4 x Analog Inputs (Mic, Line, Instrument)
- 4 x Analog Outputs (2 x XLR, 2 x Phones)
- 1 x ADAT I/O or 1 x SPDIF I/O optical
- 1 x MIDI I/O
- 1 x USB 2.0 (USB 3 compatible)
- Digital Gain control on all inputs
- Separate outputs for high and low impedance headphones
-  TotalMix FX (with EQ, Reverb, Echo)
I would directly buy the optional power supply RME NTCARDBUS-X just in case power from USB might not be sufficient, its only €29 more.

USB based, ASIO buffer sizes down to 48 samples at single speed.

4. The RayDAT, although an excellent card, but is in your case maybe not the best choice as it is a fully digital card, and you would need a Behringer ADA8200 additionally. The ADA8200 has IMHO not the quality of RME components and analog section.
The RayDAT has a variety of useful I/O ports and is in this regard a safe invest into the future.
- 36 Inputs / 36 Outputs
- 4 x ADAT I/O (up to 192 kHz via S/MUX4)
- 1 x AES/EBU I/O (up to 192 kHz)
- 1 x SPDIF I/O (up to 192 kHz)
- 2 x MIDI I/O
There are additional modules available, like e.g. a word clock module, if you should need one in the future.
Cost: RayDAT + ADA8200 = €585 + €211 = €796

5. if you have an older PC with PCI slots one of the older RME cards, maybe even from used market
I, personally, wouldn't invest into PCI equipment anymore, only if you might have an older system with PCI slot.
I only mention it as this was one of the cheapest options in the past to get those from used market.

PCIe based and ASIO buffer sizes down to 32 samples at single speed.

HDSP 9632
-1 x Analog I/O (192 kHz)
-1 x ADAT I/O (at 96 kHz via S/Mux)
-1 x SPDIF I/O (192 kHz)
-1 x MIDI I/O
-1 x Phones-Output
optional word clock module

HDSP 9652
-3 x ADAT I/O
-1 x SPDIF I/O
-2 x MIDI I/O
-Word Clock I/O
-1x ADAT Sync In

Maybe one note: the headphone outputs of the Digiface USB deliver not so much output volume, compared to all other RME recording interfaces, to put a few examples (max power per channel @32 Ohm load)
- Digiface USB:       0.1% THD:          50 mW
- Babyface Pro FS: 0.1% THD:          90 mW
- UCXII / UFXII/+:  0.1% THD:        210 mW
- AIO Pro FS:          0.1%  THD:      730 mW
- ADI-2 Pro:            0.001% THD: 1500 mW
- ADI-2/4 Pro:         0.001% THD: 2100 mW

As I already mentioned, a PCIe-based card could achieve optimum results for what you want to achieve, depending on the performance requirement of the VSTi and what system you have.
The newly designed AIO Pro has many good features, excellent AD/DA converter and a powerful headphone amp.

I would buy both products, Digiface USB and AIO Pro FS and then decide.

So, your main motivation seems to be, to get lower latencies, nothing more.
It does not even seem to matter to you, that the Digiface USB has no MIDI ports
(which you are currently using from the Motu for your keyboards).

Could you kindly share some numbers from the Motu M2?

Start your DAW, load the Motu ASIO driver and report input and output latency for all supported ASIO buffer sizes at 44.1 kHz, then you can compare it with my values here for different RME solutions.

Maybe somebody can report values for AIO Pro FS and Babyface Pro FS. Would be interesting as they have newer, faster converter. I could also add these values to my Excel sheet.

Thanks for the replies everyone, and sorry for not replying for so long.

I've tested the Digiface USB and the latency is perfect at 44.1k and 32 buffer size. However, this doesn't run stable, and to my understanding even very powerful PCs can't reliably use it (let me know me if I'm wrong).

I think a used PCIe card would be a fine solution for me at the moment. If I installed a HDSPe I would get noticeably lower latency without being forced to set buffer sizes so low, correct? Or would it allow me to select lower buffer sizes without crackling while the latency for each buffer would remain roughly the same?

Either way, I would get lower latency at similar buffer sizes than with a USB interface, to my understanding.

The computer I would use it in for now - and later probably give it away to someone to serve only for VST piano playing - would be this one: https://dl.dell.com/topicspdf/optiplex- … _en-us.pdf

Will a HDSPe card fit and will the PSU and other parts be fine? Is there anything I should know? I know nothing about these things.

What I don't like about these Pcie cards though  is that they have high output impedances, which would make them unusable with my 120 OHM Sennheiser HD 560S.

Are there options with a maximum of 15 Ohm output impedance? The AIO Pro is the only one I've seen (with a very low 0.1 Ohm), but I really don't think I should spend this much since I don't need 90% of the things it offers.

Thanks a lot!