[The Weed]

Actually, RME's drivers are truly multi-client - I have an RME UFX - and arguably the best of any interface manufacturer. His issue is Buffer Size, not Sample Rate or Bit Depth. Buffer Size has to be changed in the Fireface control panel, not TotalMix. It cannot be changed within Pro Tools. Sample Rate and Bit Depth can be changed within Pro Tools, at least with my UFX.

That said it is always best to make your onboard soundcard the default for Windows Sounds/Audio and leave your interface for Pro Tools only, even one with multi-client drivers.

What I have done to avoid any issues, at least with Sample Rate and Bit Depth, is set all my Pro Tools sessions to 24/48 and my onboard Realtek soundcard is also set at 24/48. I can always Bounce or Export at a lower Sample Rate and/or Bit Depth.

To swrecord who is using a separate interface for Source-Connect. When using S-C's Link Plug-in I was getting occasional squeaks and squawks in the incoming signal. S-C's support told me to either use S-C standalone, use a high buffer setting (512 or better, which induces too much latency for me), or, as you are doing, purchase a separate interface. Fortunately, RME's TotalMix allows me to route signals in such a way that I can use Source-Connect standalone in, AFAIK, any situation I can think of, keep a 64 buffer in Pro Tools, record myself and the other end and have a talkback mic too, even have a producer remote direct and feed them to the other end if the studio isn't set up for that, although I can't think of a studio recording me that couldn't.

TotalMix is a game changer for me, but it sure takes a bit of head scratching and brain cramping to be sure you're doing the routing correctly. I'm putting together a Word document with text and pictures to keep it straight.