By uncheck midi thru, are you talking about Options - Midi Setup - System - and uncheck 'Enabled'? I thought that disabled midi altogether. The Cubase VST 5 manual seems to be missing stuff like this.
My current setup is that I have the IAC input disabled (under 'input from'), and I've unchecked Enabled on midi thru. I tried this with and without the Enabled thing checked, and with and without a track in the arrange area. When I get SVP playing back, the audio stops in Cubase. Hmm...
There's gotta be something I'm doing wrong if you've succeeded in getting what I'm doing working right.
I'm currently not using any modem/printer port or anything. I'm using IAC or just virtual ports. If I can't get that working - midi from SVP into Cubase via IAC or virtual ports of some sort, then my next option will be using two different systems for it. If you got IAC/virtual ports working though, I think I'll stick with that. Just have to crack the code of what's going wrong first.