I know a little bit about Magnepans as you can see from my system.
Forget the amp - everyone likes to buy things. Your first order of business is straightening out your room, speaker setup, and room treatment. It's going to be a challenge as a little bigger room with different dimensions would work a lot better and you don't have much to play with. Pull the speakers out from the wall, put some diffusion behind them, and make sure there's absorption behind your listening seat. Good Luck!