Not meaning to step on anyones toes here but ...
The Denon actually might have trouble running those M80's at sustained high volume . The Denon is only rated stable to 6 ohms .
I had this problem with my Thiels over heating a Denon 5800 (Which supposedly could play satble down to 3.2 ohms tlb) and switched to Sunfires stereo amp which has been trouble free.
Also ... As a firm believer in break-in and the proud owner of M22's and M3's .... I test all speakers before and after and IMO they both definately benefitted from a wee bit of break in.
Definately not as much as some others , but benefit none the less.
At first the M22's where a tiny bit harsh and thin on the bottom end . So I took some notes on songs and played them for a few days with out listening ... then went back to them and the rough spots were gone and the bottom end seemed more natural and slightly fuller.
The M3's were identical in the highs as the M22's , but much weaker in the midrange and the bottom end although present was a tad compressed as I noticed the decays in certain instruments seemed too quick. I played these for a few days as well ... not listening to them and returned to the same music and voilà! The evened out beautifully.
The M22's in particular produce a wonderful clean clear soundstage and the mids and highs are fabulous. NOTHING like the way Drmurray described the M60's.
The difference before and after break-in is very subtle on these IMO but there none the less. I know I am disagreeing with the resident expert here ... but this is a theory I've tested over and over in speakers having owned more brands then I can remember.
To be sure these do not require heavy break-in like some speakers I've had. As an example ... My Sunfire Signature Subs (2 of them) required many many hours of break-in (Real pounding actually)... I would say easily 200 hours to fully loosen up those beasts of stiff surrounds. The difference was measurable in absolute output at various frequencies.
I argued this over at AVS ... one reviewer there tested this theory on output of the subs tested ... his findings agreed with mine and he found that indeed the output level produced a measurable change on 2 of 3 subs tested before and after break-in. 2 VERY popular subs ... mentioned in this thread.
Anyway ... I personally think the M80's would have been a better match , if for no other reason than the mismatch of driver configuration . The 750's use 4 5.25" drivers which is going to tip up the mid range much like the M22's do which produces a wonderful soundstage and fantastic detail.
I'm guessing the 60's much like the M3's may be tipped up slightly in bass where as the double mids and tweets on the 80's would have given him the detail he was looking for. That's what happens though when you compare apples to oranges.
Knowing the Vifa tweeter quite well ... I'm wondering how much he'll like it in a few months . Personally I feel it's one of the few tweeters that sounds better newer than after many months when to my ears they get flat (Or as some put it "They smooth out")
The Axiom tweeters I like a LOT.
As a musician for many many years I can say for a fact that Live is sometimes harsh or brite ... this is a fact ... Accurate reproduction will also sometimes be harsh or bright . I don't expect a speaker to smooth this out ... if it does it's taking something away that should be there. Accuracy means that SOME recordings won't sound that great because THEY WERE NOT.
But at least you are getting what was intended.
