Frank,
In GM mode the non-GM sounds are visually marked in the eventslist in OMB. I just checked the 30 styles that are included in OMB. 25 of them don't have any non-GM drumssounds. 5 styles each use one drumsound outside the GM range.
If you find styles that don't sound full and complete, then just don't use them. There are plenty of others.
Again, thinking that you can convert all styles to GM in an automated way is an illusion. Most styles that you'll find are converted from Roland, Korg etc. Most of the remaining original Yamaha styles are not XG, they use banks from the PSR550/PSR740/PSR2000/Tyros that are not defined in XG.
If you find a style that sounds interesting except for the drum track, then you can easily replace the drum track with that from another style using the import/export options in OMB.
Now here is another idea. When Yamaha makes a new set of voices for a new keyboard they also make new styles to match that new voices. You have made your own instrument the FLR2000, now you should also make your own new styles to match that. It's really not that difficult, you don't have to start complete from scratch. Copy a few tracks from styles and midifiles and modify it until you have a one-part-one-bar style. Only 2 seconds of music how hard can it be? Then it is all "copy and modify". Copy and modify to make more parts. Copy and modify to make fill-ins and intro's. Copy and modify to make the variations longer. It will take a day to do it right but you will end up with a style that sounds better on your gear then any style that you have now!
Jos