Although you would miss out on the 5% complete-system HT discount.
Not exactly true (though kinda, sorta true - see below). The discount comes in when you buy five pieces of gear - any gear. So a pair of M80s, a pair of QS8s, and a VP-150 would get you the discount.
The only way you lose any discount going his described route would be if he decided to get a sub at a later date - he wouldn't get 5% off the sub.
As to the main question, I can't comment on the M80s - I have the M60s. I think that's what most people in this forum have as well. But I understand that the M60s and M80s sound almost identical except that the M80s have a more substantial low-end extension. I think the M60s are a little on the forward/crisp side. They can be tamed with proper placement, though. On the other hand, I only ever really heard it with questionably recorded/produced material - then there's a little sibilance. I didn't and don't ever hear it with well recorded female vocals or well produced tracks generally...
