Are you using MTC/SMPTE sync? Playing the 880 and Cakewalk back at the same time with one of them the master and the other slave, and connecting them with midi cables? If not, you're missing out on a lot of flexibility.
What I do is get the form down in Cakewalk. Do a few midi tracks and then record guitars, vocals, etc. to the 880 while they're in sync. To free up tracks and effects on the 880, I'll bump 2 tracks at a time (in sync) into Cakewalk. If your soundcard has a S/PDIF input, you can do it digitally. Then with everything on the PC, you can mix down in Cakewalk if your system can handle it. If not, yeah, mix your midi to two, not one, tracks(R/L) onto the 880 to get a stereo mix.