These two pairs of speakers are very different. sounds like you like the M3s better. It is a mistake to assume that the more epensivve speaker should sound better.
The Graham is indeed less sensitive but more power may not make it to your liking. I’d try to borrow or audition an amp before I spent $10000 hoping it would sound good. That is a way to send good money after bad.
Where are you located? I’d love to hear the spatial audio speakers in my system.
Jerry