So the thing about sysex is that you need to include a value -- a V in the sysex bytes -- to allow it to receive values properly. You might be able to pretend one of your bytes is a V in case your incoming sysex does not actually contain a variable byte or bytes, but anyway... give this a go and see how your experimentation moves forward.
Thanks!
Dan
Dan Rosenstark, Author & CEO
MIDI Designer :: dream | create | play