So it sounds to me like you've got an ENFP with his Ne in overdrive (aka not implementing new information because he's too focused on taking in more new information) and an Fi function that's giving push back because for him to change he'd have to do a rethink of his Fi vision of himself as a band member. <- Never pleasant, but a required skill for a mature adult.
If I'm right, then my advice to you is some direct confrontation but done in an Fi-friendly manner. When my Ne gets into overdrive, you've gotta right it down on a post it note, tape it to the end of a 2x4, and whack me upside the head for me to get it. As far as how to have an Fi-user friendly conversation... #1- talk to him in private. #2 - Remind him of his other Fi values. There are Fi values, then there are Fi values. In other words, tap into a more important Fi value, and he'll do an Fi rethink on his behavior.
For example, I may want to be able to express my Fi-ness and be true to my vision of myself. (<-Current Fi value driving my behavior.) But I would be horrified if I were reminded that I was working against the bests interests of the band, or if I thought I was being inconsiderate of other band members. (<- Higher Fi value I'd realize I'm violating.) If I were in the ENFP's shoes then I'd probably burst into tears and then spend a week apologizing to everyone. (That's another thing, don't expect him not to show his upsetness. Just remember he's probably most upset with himself. Let him be upset and work through it himself.)
Hope this helps! Let us know how your ENFP problem progresses.