The key point here is that the motu interface is class compliant and every setting is web based (if you need to change anything) you get the best of both world's. 100% usability and no need for that extra mixer to carry. I have lots of audio cards, FF800, Focusrite Saffire Pro 40, Pro 24 DSP, Presonus FP10 and various USB cards to name some of them and all of them works but on board DSP features are not possible to use unless on Windows or OSX.
The Motu AVB line is the first I have come across where everything is accessible from ANY os including onboard reverb, busses routing matrixes and so on. No monitor mix latencies since it is hardware. I was considering a smaller formfactor RME for live performance but stumbled on two Ultralight AVB cards for the price of one and this is a game changer so I wanted you to get my point.
I use it mainly as a plain interface but if I need to record a vocalist. I just set up a mixer with a few channels and let the vocalist adjust the monitor mix without affecting my recording. Give him a small amount of reverb in the monitor mix (that he then can adjust for his liking) It is too easy not to check this out. If the vocalist has his/her own ipad, they get their named faders to adjust accordingly. The possibilities in this little card is close to what you get with a full blown mixing console like X32 or Presonus Studio live console. RME is great but this flexibility is not their strength at the moment IMHO.
/Anders