You need a better amp, not necessarily a bigger amp. Either way, no 2 companies rate amp power the same way, so its hard to compare. A huge step up would be an Ayre V-5. If you feel that you need more power, you can just get a 2nd one and do a vertical biamp. The original M series are very laid back. So much so, that you don't want to do anything to enhance that aspect of the speaker.
If you're really concerned about power, they maybe a good used Theta Dreadnaught. Either series 1 or 2 is fine. Not the new class D version. You can use 4 channels and vertical biamp.