Emu XL-7 & MP-7 User's Group

Hello ; I said I loved the sounds of this box but I must say it takes
a hell of a time to understand how to make it work properly !!
So... I don't like to ask help again but I'm stuck and so frustrated
not being able to think about music ...I'll stop moaning 'cos I know 
there must be a (simple)answer somewhere and I'll feel ashame again!
Here's my problem : I want to be able to play the patterns
 (cha.1 to 16 A) and at the same time adding something from my guitar
-controller (GR30) which is supposed to play on channel 1B...in the
midi menu I put  omni enable, receive prog.change on for theA and off
for theB channel, rechannelize midi in :off , merge midi : off and
tried so many alternatives to get to the same problem : the pattern is
playing fine but when I change the tracks/chan. the sounds (of the
snare or the bass drum )are changing accidently as well  so playing a
syn(or any)sound on chan.1b add suddenly a ton of reverb on the other
(rythmic) channels !   Au secours!!