Sorry, but I can only answer questions that make sense and that can be answered.
The concrete requirement sub 2ms RTL you delivered later. IMHO, this has nothing to do with the card itself.
This I tried to explain to you, that internal digital processing inside the card (in the FPGA) has the lowest latency, also digital transport over digital transports like ADAT or AES.
What I also did not understand that you elaborated on the RayDAT as if it would be a MADI card. I do not understand what you mean by this. This is simply not the case. It's a PCIe card without any analog converter. So, it also makes no sense to elaborate on the RTL of this card when it has no analog A/D and D/A converter. It depends on the HW you connect to it through ADAT.
Also irritating, you mention so many interface cards, with different number and types of ports, that it really makes no sense to compare these to each other. Especially as the latency inside of the FPGA (internal processing) is IMHO not that different. What has more relevance / effect is transport to PC and back (most) and converter latency (if the cards have any analog I/O).
The highest latency you have anyway with the transport to the computer and back. With RME there is not much difference between PCIe, USB, FW, TB. RME doesn't use 3rd party chips, all is done by the FPGA.
To put an example with a product that I know: the lowest RTL (incl. A/D and D/A) you get with the UFX+ over thunderbolt, but RTL is still around 2.6ms.
I have some doubts that you will find any solution which gives you sub 2ms RTL (incl. A/D and D/A).
The next questions are: for how many channels and at what sample rate.
You might know that A/D and D/A converter latency is a little (!!!) bit lower at higher sample rates.
But by that, you put a severe workload on the computer.
I have doubts that you can get a stable setup that works permanently at sub 2ms for everything.
And for what you have this requirement? I can without any issues play Guitar over a virtual amp with a RTL up to around 13ms, better is below 10ms. This you can achieve with an UFX+ when using an ASIO buffersize of 128 samples at single speed.
If you talk about MADI, when multiple devices are connected serially, the MADI I/O of each OctaMic XTC causes a
delay of 3 samples at single speed (6 at double, 12 at quad speed).
Here is a list of RTLs of different products: you can see that the different transport methods are not that different (USB, FW, TB): https://www.tonstudio-forum.de/attachme … es-v2-jpg/
Maybe you should better start to describe your requirements and use cases.
I think it's more relevant, which devices you need to connect (so what number and types of ports you need).
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13