[Updated]

What is your maximum budget for this?

Why only 4 ports? Don't you need a port reserve?
If you look in big shops like e.g. Thomann, there are more models that follow an 8-port scheme (-> more choices for you).

Do you want to connect the preamp analog or digital (ADAT, MADI).

I ask because you have more digital than analog ports on your UFX+.
- 8x analog I/O completely independent of the sample rate
- 1x AES (2ch at any sample rate), 2xADAT (16ch at single speed), 1xMADI (64ch at single speed).

I think it is very likely that you will want to use the analog ports on your UFX+ for purposes other than connecting a 4-port mic preamp. For example, you could use them to connect high quality reverbs or other external devices.

Digital connection: ADAT or MADI?

If you are connecting a digital preamp, you should consider whether you want to use ADAT or MADI.
You only have two ADAT connections on your UFX+, which you might need for other purposes in the future.
ADAT also has a certain length limit of 10m according to the standard (in my setup up to 16m is possible).
ADAT has only 8-ports at single speed (44.1/48). The number of channels is halved at double speed (88.2/96 kHz).
This is also true for MADI, but starting from 64 channels (higher reserve).

You have the highest channel reserve with MADI (64ch with Single Speed, 32ch with Double Speed).
If you don't plan to use devices that use all channels of a MADI bus, like M-32 Pro AD and M-32 Pro DA at Double Speed, then you have the best scalability possibilities with MADI.

Another advantage of MADI is that you can connect many devices serially and each of the multimode fibre cables between the devices can be up to 2km long. OM3/OM4 patch cables are usually available up to 30m, and some shops even offer 50m.
Higher length you have by structured inhouse cabling in bigger buildings/studios.

So if you are using this setup at home or in a studio, then a MADI-based setup would give you more flexibility by placing the preamp closer to the drummer's room, then you can use shorter XLR cables to the mic there and also give the drummer a submix for headphones. Same on stage if you want to place the preamp closer to the drums. Then MADI acts like a multi-core cable. A little disadvantage of MADI: the units with MADI support cost a bit more.

RME preamps with RME specific options:

- Auxdevice support
Devices like the Octamic XTC support Auxdevice support, which means you can control them remotely with TotalMix FX and save/recall the settings in a TM FX snapshot, which is very convenient to get proven settings back quickly.
Unfortunately, the Octamic XTC is currently no longer commercially available.
And the new model, the 12Mic, does not have the auxdevice function built in yet. Some customers like me have been waiting for it for about 2 years. Everything seems to be delayed a lot because of Covid. It's still promised.

- Autoset
Nice feature that either helps to quickly find the right gain settings or makes sure that the gain is automatically reduced at higher peaks.

- Delay Compensation - only with the Octamic XTC - for RME preamps with MADI and following an 8-port scheme.
If you connect several XTCs, then the Delay Compensation ensures that the audio signals from each of the preamps arrive at the UFX+ for monitoring and at the DAW for recording at exactly the same time.

- EDIT: Steadyclock. RME's Steadyclock technology makes RME devices/preamps to ideal clock slaves removing any clock jitter and performing AD/DA conversion using it's own internal clock.

Other things to consider

• If you are satisfied with the very good and transparent preamps of your UFX+, you should consider getting an RME 12Mic, because the preamps of UFX+ and 12Mic have according to RME the same preamp design.

• If you are recording drums, then it can be an advantage to either have preamps with PAD to prevent overdriving one input, or to get mic preamps that have enough reserves for stronger input signals.

• There are also preamp designs with inserts (send/return) in the analogue path, should you need this. With RME you can route signals through the digital matrix to insert external devices into the signal path.

RME - high quality, transparent conversion

Which speaks for RME preamps like XTC and 12Mic is the high quality transparent conversion of the original audio signal.

XTC - connection variety, even 2 headphone outputs, even ADAT/AES I/O, format converter between MADI/AES/ADAT, class compliant audio via USB (e.g. to be connected as preamp on an iPAD). MADI features like delay compensation. Auxdevice support, 4 ports support PAD, 4 can be used as Instr inputs (Hi-Z).

12Mic - latest preamp design like UFX+, high gain (+75dB), level resistant inputs, 3x ADAT I/O, 1x headphone output. High port density (12 ports in 1 RU), with MADI and AVB support well prepared for any connection demand. Capability to integrate MADI components into an AVB network. Mic input 1-4 can also be used as Instr inputs (Hi-Z). Auxdevice support for the 12Mic is promised, but not yet delivered (*).

(*) As a workaround you can use the MIDI Remote for 12Mic (and AVB Tool) which has been introducted here: https://forum.rme-audio.de/viewtopic.php?id=33276.. In situations where you are missing LAN or Wireless to remote control 12Mic through Browser (like e.g. Firefox) you can remote control the 12Mic through MADI using this little application. This compensates the lack of Auxdevice support at least a little although the implementation in TotalMix FX would be nicer, because then you could save the preamp settings in TotalMix FX snapshots/workspaces.

Additional information about setups with RME preamps from my blog

UFX+ and Octamic XTC via MADI: https://www.tonstudio-forum.de/blog/Ent … cber-MADI/
UFX+ and 12Mic via MADI: https://www.tonstudio-forum.de/blog/Ent … XTC-DE-EN/

Regarding your only requirement

You told "Mainly for recording live drums".

Drums produce a loud/strong signal. So you should not need to worry about gain reserves of your preamp.
Nevertheless a preamp of high quality, less noise and input level stable inputs is a good investment for any project and for the future.

Besides looking at technical data of the preamp section you should also look at operational and investment aspects and sustainability:

• What preamp fits best into your setup (same high quality preamps as UFX+, remote control options, ...).

• Consider cable length (MADI, AVB) and by this a big flexibility in placement in the studio and on stage (MADI can be used like a multi core)

• Options for remote operation (LAN/Browser, MIDI remote via MADI)

• future proof (MADI and AVB support), long term driver/firmwar support

• port reserves

• port density (all very compact in one rack unit)

• very detailed documentation incl. technical data

• very good vendor support through forum

Investment protection: buying too small is lost money.

Talking further about sustainability: at the end it's also better for "mother nature" if you invest into products with a long product live cycle like RME devices. If you should need to sell you even get much higher prices on used market for such products with excellent long term support (driver/firmware).

More specific recommendations

I gave you this overview so that you can make some thoughts, what you want / need.
More specific recommendations can only be given, once your budget, operational / technical requirements are clear.