I got word from M-Audio online support that none of their interfaces support multi-client operation.
I have read testimonials from users who use MOTU 16A and MOTU M6 and say those do support it.
I have also read that all Native Instruments devices also are true multi-client.
All Steinberg interfaces are true multi-client as well as RME.

@Matt:
One thing you can't do without multi-client is record the output of one application in another. It is also super convenient to have individual applications routed to dedicated I/O of the same interface. For example, in my RME TotalMix (RME's software mixer) I have dedicated channels for Windows audio, BiaB, Guitar Rig, 4 channels from my DAW, etc. All with individual volume faders and routing options.

Last edited by Chicago; 07/10/23 10:16 AM.