I have the SD-50. Refer to page 59 in the Roland SD-50 Owner Manual (black manual). Turn on the "TG to Computer" function. This will loop the audio output of the tone generator back up the USB cable to the PC. You then have both the MIDI and Audio available to render with the BIAB software.

I haven't actually tried this yet, but will do so in the near future. I'm still a little confused about rendering with the BIAB 2011 software.

Let us know how this works out.

Dave R