So I was able to simulate the hack with mednafen and medgui. Some comments so far :
1) The music doesn't stop when it's supposed to when you die
For that short period, for the megaman dieing sound? I didn't bother muting the CD track, 'cause I didn't think it was such a big deal. But I'll put that on the list. That, and all system bios calls (for handling CD audio) pause the emulation. That would be very annoying. I'll have to see how I can replicate that specific bios function, inside the game code.
2) Similarly, the music doesn't stop when it's supposed to when a boss dies
Same as above. I'll put it on the list of things to do.
3) This is purely a matter of opinion, but I think it'd be nice if some of the short songs, such as "boss selected", "game over" and "victory" were still chiptune.
I can add that function to the options menu; pick which is played for song # - cdda or psg. Though one could just easily make PSG tracks for that in wave format.
4) Is this based on the PAL version ? There is a low pitched noise after the shooting sound effect.
No. It's NTSC. Sweep emulation isn't.. emulated yet. From what I've read, even though MM doesn't setup those regs, it doesn't initialize them either. I suspect it's from that, because from everything else I've checked - all period values fall exactly inline with what they're supposed to be.
I'll be converting the sound FX into a VGM style format (time based period/reg updates) pretty soon, and get rid of ~all~ APU emulation (replaced with custom PCE sound driver). That'll be the first thing I'll clip (that trailing sound from the weapon fire).
5) The "stage select" music was SOOOO much better in the old version. Why change it ? This one is VERY lame, and is wrong
6) Even though the Wily stage music got replaced, Wily stage 2 music is wrong (it's from Mega Man 3), and anyways both sounds way too much heavy metal to me. So my comments about Teck's versions still apply.
I personally think MM music as rock/metal sounds good to me. It fits for me, but there aren't enough cover tracks to fit. The game is distributed into two separate parts; CUE/ISO and Music pack. I was never happy with all the tracks, rock/metal or not, so it's up to the individual to replace the tracks with whatever they want. They're wave files; easy enough to do.
7) Is there a way to make the music loop more elegantly than fading out, stop, and fade in again ?
Edit the wave files. All the fading and space between looping is in the wave file itself. If you use absolute start/end of the wave file, you'll get tight looping.
8 ) I really hate hate Ice man's stage. Oops this is not related to this hack, sorry ^^ This'd be the easiest game of the series if this weren't for Ice Man's stage.
The flying platform part? Just get the beam/platform item from Elecman's stage; it makes Iceman's stage a breeze. The only hard parts in the game, IMO, are the Blob boss and the MM clone boss (relative to the rest of the game).
MM update: Cutman's enemy sprites are now all converted over - https://www.youtube.com/watch?v=5i48xMQX7NI
Still tweaking the MM animation (running frames need more tweaking).