Hello Mark,
To update the earlier comments, I've downloaded the Owner's Manual for this device which has substantial info about the Midi implementation.
Firstly, I note that the SRX stuff relates to the expansion cards, not the main unit, so this may not apply.
I note that the main (accessible) sounds are listed as GM, but these sounds are actually structured as GS, i.e. they are accessed using LSB and PC with a fixed MSB. There are also a number of non-standard banks (User and Preset A, B, C and D) but I see no indication of how these are selected via Midi. Maybe I need to read the complete manual to see if this is possible, but it may not be.
Which sounds were you hoping to be able to use?
Of course, even if it is not possible to access sounds in the usual way, there might be options using SysEx, which could still be used within a SMF (Standard Midi File), just a little more complicated.
Geoff