Hi it's me from the future, MAME now properly emulates all the games 1st-EXTREME, the SuperNOVAs are emulated with another emulator (a specialized fork of PCSX2)
Can the characters be selected ?, I already have them running the extreme, max 1 and 2 with everything unlocked but I don't know how to select the dance characters.
Unfortunately, every single emulator can't emulate rhythm games accurately as they are ALWAYS out of sync. PSX, PS2, MAME,... all of them can't go in sync so the best option will be always Stepmania...
i'm tested ddr extreme on mame 0.211(latest version) and it works, see "whatsnew" on the official website mame and search "Konami System 573 MP3 playback"