Actually, most people would be delighted at what you found. You can record multiple simultaneous channels on Mac, but not on Windows. 
Audacity can’t do any track to channel allocations, so you would have to do them in the Terratec and be prepared to record empty channels if necessary - that is, set Audacity to record six channels but only send it channels 3 and 4.
To emulate Windows you could perhaps try uninstalling the Terratec drivers but then of course the device may not work at all.
Gale