You need the aproppiate SYS-EX message to activate Ch#16 as Drum Channel. This SysEx is recorded in midi file every time when you do some recording on G800's recorder. I recommend you to use this tip (I use this also on my G1000):
- Insert a floppy in G800's drive
- In G800's Recorder section press Record, wait one second and press Stop. G800 will ask you to save recorded material to disk; Give some name to file and save it. It appears you didn't record anything, but you recorded the SYS-EX informations, control and patch assignments (known as Header) along with Midi file.
- Now insert this floppy in your PC's drive. Import the file you recorded on Roland (as .MID extension - standard midi file format 0) into CakeWalk. You will see that all the data was recorded in just one track. Mark the whole recorded region and do "Remix" from Menus (I work in Cubase, but hope Cakewalk has same option). After that, you will get 16 midi tracks. You have to delete the original track (which is remixed).
The rest of 16 midi tracks you can now use as Midi Header. Just open some part at beginning of track and you can edit many parameters (such as Volume, Reverb, Chorus, Program Change...). In first part on the Ch#1 is SysEx you need, and every time you playback just-made header, you Roland will automatically set up Ch#16 as Drum Channel.
If you want to set-up the specific reverb/chorus setting or patch on specific position, just copy the first part (bar) of it's track, open it and edit the data. Never delete these control parts.
When you finish the work, you may freely export it as SMF (.MID) and play from G800 for best timing. Don't forget - G800 may manipulate songs with max. of 17 tracks - no more!
You can't sequence all 32 parts from the keyboard. You must have a computer or sequencer w/ two Midi ports to do that.

Good luck !