I still think you’re better off hacking a PS1 pad and using this adapter:
Cube Joybox Pro
http://www.play-asia.com/paOS-13-71-g4-49-en-70-14p.html
Works flawlessly with my MAS and my hacked DS1 custom, and I can still do PS1/2 fighters and PS3 fighters with Laugh’s inPin adapters.