Yamaha DTXpress/DTXplorer/DTXtreme

I know that this has been mentioned before, but looking through the 
archive I could not find a definitive answer.  The memory available 
for loading MIDI files as User Songs seems to be very small - I only 
managed 2 songs before the dreaded "Memory Full" message was 
displayed.

Does anyone have any tips for getting better use out of what could be 
a very useful function - I have tried loading Type 0 files (all info 
on one track) and Type 1 (info split between multiple tracks) but it 
makes no difference. 

Maybe someone knows the exact amount of memory available so that if I 
have to, I can edit each MIDI file to the bare minimum before loading 
it, so that I can get more songs ?

Thanks very much

Kelvin