Side note: the HDSPe MADI card is a PCIe card (not PCI).

No benefits. In the digital domain, it's simply lossless transfer of digital audio data (“zeroes and ones”) up to the D/A converter. It doesn't matter whether the recording interface is connected through USB or PCIe.

At the D/A converter, special RME features like "SteadyClock FS" can give you additional benefits. I put together some interesting videos in my blog: https://www.tonstudio-forum.de/blog/ent … ses-en-de/
Direct links to the YouTube Video about SteadyClock FS:
English version: https://www.youtube.com/watch?v=Ti0aHW-zYcs
German version: https://www.youtube.com/watch?v=6rcBVuWOHiw

An RME devices with SteadyClock FS is the perfect “clock slave” in a digital audio connection. By SteadyClock FS technology, they get a lock very fast and hold it reliably. You will see it in the video, even with a heavily jittered connection and such a high amount of clock jitter that you would not see in a real-life situation. And of course also not when using the components / signal chain mentioned above.

Another benefit of RME converters like ADI-2 Pro and DAC FS is, that after refreshing / “purifying” the clock signal by SteadyClock FS the final D/A conversion is being performed by the internal FS clock.
So, the D/A conversion inside ADI-2 DAC / Pro is fully decoupled from external clock signals.

To sum up: SteadyClock FS takes care to remove any clock jitter from a digital connection and to get a lock on the signal quickly and to hold the lock/sync reliably. The D/A conversion in the ADI-2 DAC/Pro is being performed by the internal precise FS clock independent of external clock.