Recording chain question Mixer to Delta 66

[kybdplr]

Recording chain question Mixer to Delta 66
Have a Behringer MX1804 12 channel mixer & an M-Audio Delta 66
4in/4out sound card. HAve four stereo channels from keyboards routing into the stereo ins. The PC output 1 & 2 goes to the tape/two track input. How do I route the signal from only one channel into the PC's input 1 & 2 without the bleed from the PCs input ending up on the recorded track. I was told by Behringer tech support to use the Alt 3/4 outputs which works great but when selecting the 3/4 buton to route the track to be recorded it mutes that track from the main mix.

HElp...anyone else have this setup. or any online site to see typical singnal path or mixer setups?

James