This one is easy.

Just record the output of the SD50. This can be accomplished any way you want.

Also, you have it backwards. The sound passes through the SD50 lastly (BIAB to SD50), and results in the finished product at the headphone jack.

This question is silly......really LOL

BTW, I own the SD50 and it is the best portable synth Roland has made yet. It even runs on batteries: It is USB powered, an Audio interface, plays MP3's and Midi files, is small and light, and will even loopback (apparently, as the previous poster said, and something I also haven't tried). Did I mention it sounds great?

Kudos to them