I've been hearing a lot of complaints regarding the Muse-On controller, specifically more towards the length of the springs used under each button.
Apparently the strings provide way more resistance than necessary, making Trilogy an unecessary pain to play. I can't imagine playing IIDX with buttons that take significant effort to push down; not without developing some kind of wrist/hand injury.
Ask the DJMax board, they may be able to provide more feedback on the subject matter.
I do remember looking up a guide though of someone dissassembling a Muse-On while attempting to modify the button springs so that they became less resistant, but I can't recall the URL for it. You might be able to Google it up, or someone from the DJ Max board can link it to you.