The MR from the bard buffs seems to go outside the mr cap. I *think* the mr cap is from suit based items.....and it seems to poop the bed around 20-22 from what I remember.
Wisps give a bump of mana (12, maybe?) every so often. Lich form increases mr, but i've never really tested it as far as the mr diminishing returns and whether it applies.
I was honestly just trying to think of everything to jam more MR on. If you are doing something specific that requires a trash ton of mana, this would be the way to go. Obviously, I wouldn't build a toon around this, but if you can swap stuff on/off on a pretty modular character, why not duece it up?