Multi Mode..
Imagine I make a patch like this..
1) Midi channel 1. ROM A-032
2) Midi Channel 2. ROM S-001
3) Midi Channel 3. ROM C-010
First thing you do is disable the "Mutli Prog Change" in the config menu as it has a habbit of pissing you off
OK you're in multi mode , you have a 3 patch multi. Go into multi-edit [SHIFT+EDIT] and turn off all the unused channels/layers in the "Part Enable" tab. In my eg. they would be channels 4-16. [You scroll through the different channels/Layers with the < PART > buttons above the MULTI / SINGLE buttons.]
You select the Bank and program with the knobs.
Page 2/3/4 are general settings for the selected layers outputs, volume etc.
Page 5 is for making splits, for eg. Assign a bass synth on channel 1 to play notes C1-G2 and then assign a pad on channel 2 to play notes G#2-C5. That way they will never overlap when you play on the one keyboard.
Easy enough once you realise the basics :-
SHIFT+EDIT to get into the setup
Part < > buttons just scroll through the different layers from 1-16
Turn off the unused layers
Keep layers on the same midi channel to make big sounds/splits/drum kits etc to play from 1 keyboard.