Ugh, so many hours wasted messing with this, it's fun thou
Should just use whizzy's stuff he's already made, they sound close enough, lots of orchestra hits is the main thing
I haven't made any proper remixes yet, I've spent most my time trying to sort out the samples so I had a library of sounds, but I have most of the main instruments ripped properly and saved if you guys need them.
Building a soundfont is too much work, the samples work better in modplugtracker without as much fuss.
I've been converting spc's to .IT files and importing into modtracker, the samples sound perfect, but when you use them on songs the midi tracks themselves affect how they sound, so it takes a lot of work to transpose everything and get it right.
Here is a test run of the tmnt3 boss music, it needs a ton of work thou, but gives you an idea what you can do using samples, and also how much work is needed. Was hoping to be able to just replace instruments but he midi's really need reworking to make them sound good.
TMNT3 miniboss
https://www.dropbox.com/s/brbawehvw4zm4mm/TMNT3-miniboss.mp3
I haven't been able to find any better midi's, I even tried to start ripping the midi's from NSF files, but it's another pain in the ass and takes ages.
Just for fun I also did some TMNT NES ones to test how they might sound. Just note that none of these are proper tracks, they would need lots of work, just some test runs with little tweaking. Some don't even have snes drums yet. Biggest problem is usually the bass as you can hear.
Overworld Theme (TEST)
https://www.dropbox.com/s/8504f86oaaptjqb/T_TMNT_OverworldTheme.mp3
Dam stage (TEST)
https://www.dropbox.com/s/96pbncwmenssul9/tmnt-dam2.mp3
Bronx (level 5) (TEST)
https://www.dropbox.com/s/0xmcjfpuuhezneu/TMNT%20NES%20-%20Bronx_2%20-%20TEST.mp3
Sewer Stage - (TEST) warning this one has some real bad probs with some instruments.
https://www.dropbox.com/s/13qmbs61zntck0k/TMNT_Sewers-TEST.mp3
Anyhow gives you and idea what they they'd sound like done properly.
@DIF - Ok I might give it a go, I'm kinda failing on this so far

I'll have to rip more midis, vgmusic only had a few for tmnt3.
@Uche - The original TMNT Arcade version music matches pretty well the tmnt4 snes music so can just rip that.