Lapolla seems pretty poor (hiccups and crackles a lot) for anything other than the most simple MIDIs.
What I don't understand is, the hardware specs for the GP32 (see for example: http://gp32eu.com/system.html), specially state that it has "16Poly S/W MIDI Support".
OK great, so how do I access those 16 MIDI channels then??
Lapolla does NOT use synth channels, it uses the 4 WAV channels to digitally sample Gravis Ultrasound intrument patches... it's basically a port of Timidity, a realtime MIDI-to-WAV converter.