Try moving notes a few (1,2 or 3) ticks before the beat in some tracks (maybe just one track is enough). This way you don't clog the MIDI "Highway". Remember that the JV/XP uses up tp four oscillators per voice (that equalls to 4 voices per note on). I donīt think the effects processor has anything to dp with it. Also try setting the voice reserve parameters (in the Roland) accordingly to the needs of a particular performance.