About a year ago I used Splashtop from my iPad to control MC on my PC. Worked really well, but I didn't reinstall it when I did a clean install more recently, mainly to minimise the installed programs on my HTPC, but also out of laziness!
I assume you're using splashtop because you access the PC without a monitor.
There is, I'm pretty sure, a setting in Splashtop to not divert the audio to the client. I seem to recall that setting the audio of MC to the exact output device you want to use rather than 'Default windows device' or whatever it's called also helped in my case. I think this was because I tended to 'remote' into my HTPC with the receiver off (which should be the default audio device) and because windows saw a new audio device in splashtop it reverted to that as default (presumably because it could find no other).
Anyway, it's been a long time since I fiddled with splashtop and it may have all changed by now!
SBR