the omni that is offered by mucians friend appears to come with it's own soundcard. or am i seeing this wrong?
if it does, then i would assume you can use both cards simultaneously. i've recorded guitars through my delta while recording vocals through my onboard soundcard at the same time.
[edit]
here is the omnistudio, which comes with the delta66 soundcard.
here
here is the omni, which is to replace a 66 or 44 front end
here