@tepples
Right now I'm looking for a possible solution with famitracker so switching to famitone/pently is not an option for this project. Maybe I can test pently on a new one, someday
@dougeff
my current engine actually bank switch the driver and the song in the nmi so this part is already done. All songs are split to avoid size issue. The problem is more subtle and may have not been clear from the message: one song is actually 9k

It's not something that would be used during game play but for that specific case, I'm trying to find a way to play it without having it to be edited in some way. I need to recheck the mmc3 specs but since I cannot really put the driver in the fixed bank, I guess I won't be able to play that one, or the 35k medley ^^;; (I'm not joking, it's that big, so that one is out of the question haha).
So the only way would be to put the driver in the fixed bank to allow the song to be played, or a way to play compressed data but.. that would means to adapt the driver for that and I don't think I have the time or knowledge to update it. Hmmm... If the data is set at $a000, it would spill a little bit in $C000.. That's one possibility.
I'm not in rush yet for that edge case so I will look at all solutions that can be done before doing that

The cause of the size is because it's a cover and to make it as accurate as possible, the data became quite huge. Not much I can do for now.