I think you should connect your Virus ti using usb to take full advantage of the integration thing, that's quite an advantage to anyone's workflow.
You can get away with using the Virus (I'm assuming you have a keyboard version there, right?) to control the SH2 through midi (nice synth btw). but would make more sense to me to connect the SH2 to the audio interface's midi so as to be able to use them at the same time and have them both play sequences from your daw and being able to tweak them while listening.
But the way I see it, you'd be out of midi channels by then and you still have your drum machine to plug-in.
Easiest way to solve that would be getting a midi interface with more channels, might even be from RME (since you own the sound card) since they have this really cool word clock that makes midi super tight (synced to host tempo without drifting!)... Not sure what exact expansion you'd need to get, but that's what I'd do if I were you!
Of course that you can always count on the midi through connection on the Virus, for example to trigger the drum machine, specially if it's a loop based one x0x kind of thing (unlike NI's Maschine or Akai Mpc where sequencing the drums is a little different, more focused on groove instead of placing stuff on a grid), you'd only really need it to start playing your patterns in sync, so that translates into a gate on/gate off message that a single midi through connection would provide.
Cheerios
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