Mat
I use Cakewalk, but I would think the procedure would be similar. There is a helpful document on Roland's site that solved a lot of problems for me. It's called "Using the XP-50 with an External Sequencer". I have an XP-60, but the menus are similar enough (i.e., between the XP-50 and XP-60), that I could figure out what to do. I set my XP-60 on Performance Preset A-12, "POP SET 1", which has each of the 16 parts set to a different MIDI channel. Then I use Cakewalk's track properties dialog to set the patch. Bank select method = Normal. I can select any of patches in any of the banks, including the expansion board I have installed. When I change the patch from Cakewalk, the part changes in the POP SET 1 preset (as shown by an asterisk by the name and by the name of the patch in the part changing as well). Hope this helps.
Rod