I have a (now rather old) Roland VS-1680 and Doggiebox is my drummer :) For my set-up, the best technique _seems_ to be to assemble a basic percussion track in Doggiebox, export it as an AIFF, playback the AIFF and record it on the 1680, then record guitars, etc. on top of that. The trick is that I often want to change the details of the percussion track as I work on the song (add fill here, extra cymbal there), but it's difficult to synchronize the start of play to rerecord the drum track directly (thus my MIDI feature requests some weeks back :) It works out (at present) a little easier to simply slap a whole new AIFF over the original percussion track on the 1680 to get it on the machine and roughly in place, and then "nudge" the whole thing into synchronization with the other instruments. It's still a little tedious, but not impossible.
I do basically the same thing, except that I've found it invaluable to add a measure of "count off" cymbal hits before the drum track starts. This ensures that the other tracks start at the right time and allows you to swap out the drum track with no ill effects on the timing of the other tracks. I use Doggiebox to create the drums, or at least enough to outline the completed song structure. Export it as AIFF and import into tracks 1 and 2 in Deck LE. From there my guitars plug into a Zoom multipedal box that plugs into an Eidoral UA5 USB audio hub. Guitars (and bass and voice) are recorded in succession and as long as you monitor in the analog domain (set Deck to use the UA5 as both input and output, plug headphones or monitor speakers into the UA5) there are no latency issues. I have not noticed, nor attempted to notice, the metering difference between Doggiebox and Deck that other users have noted. Cheers, Christoph PS. Ben, Doggiebox was the godsend app I've been searching for, I love it!