AK as a souncard, recording Main L/R

Hello,

I’ve been using my AK as a sound card recently, as I don’t have another one right now. I’m very happy that I can record direct synth tracks, but I have a problem I cant work around right now:

If I want to live record some playing, from the Main L/R channels (so I get FX), while monitoring, say, a beat from my PC, then the beat is recorded along with my synth playing. I guess this is obvious because the audio from the PC is also playing on Main L/R, but it would be really convenient if there was some way to route JUST the audio from the synth (including FX) but NOT incoming audio from the PC. If that makes sense.