If midrange clarity and overall cohesiveness are the criteria, I'd opt for the M3Tis and EP125, but only by a hair. You will have greater flexibility in placement and the ability to compensate for any upper bass thickness that might result from standing waves in the room or nearby boundary effects. And the sub's level control will enable you to fine-tune the balance between low bass and the M3Ti's upper bass and midrange. Plus, the sub's built-in power amp will help you achieve "crankability" when you want it without straining the rather modest resources of the 45-watter.
Since you'll be listening across the short width of the room, your amp should have enough power, so long as don't want to achieve disco levels.
Of course, the M50ti is a bit more sensitive and will produce louder sound on a given watt of input than the M3Ti's. And it will yield greater "crankability" from the rather modestly powered amp. But with a floorstander, you do have to deal with possible floor/wall interactions that may overemphasize upper bass (and lots of listeners like that effect, but it makes male vocals "fat" and sometimes heavy-sounding). A foot clearance from the wall should be ample. It might be interesting to see what Ian, the designer, thinks?
As to the source-quality discussion, I don't dare venture onto that soapbox for the moment.
Regards
Alan Lofft
Axiom Resident Expert
