Bob, replacing QS8s with QS10s is really a no-brainer. It's a night and day difference for both music and movies. I've used them with M3, M5HP and M100...all v4.
I suggest you trade in both pairs of QS8s for a single pair of QS10s for side duty. When you get them, you can experiment and if you find you still need rears (which I very much doubt), you can keep one pair of QS8s or buy another pair of QS10s.
With your M100s, if they are v4, you really don't need sides for music (movies and concerts for sure). The mids and highs are very dispersive and should envelop your listening position with crystal clear sound. My M5HPs do that also but in a smaller sort of way...which I actually really enjoy!
Your room is smaller than mine and my M5HPs fill it and there is no need for M100s. In some ways, the M5HP image and sound better. Maybe it's easier to focus images with fewer drivers and smaller cabinets. Keep that in mind because when Axiom introduces active M5s, you may want to strongly consider trading in. I know I will be based on what I know of them so far. Of course you won't have the dynamic capability of the M100s but do you really need it? I know I don't and I'm in a larger room.
I'll also say what Axiom has accomplished with the v4 is simply amazing. The M3, M5 and M100 all soundstage very similarly which is wide, deep, tall with images you can see on well-recorded tracks. The differences are dynamic capability, quality of sound across the spectrum and degree of dispersion. The M3's lows are not as tight and the mids and highs are not as clear as the M5 and M100. The M100 has clearer highs, lower bass reach and is more dispersive with its more numerous driver complement. The M100 highs are truly better. In Holly Cole's Train Song, the faint bells are more present than the M5 and moreso than the M3. Even though the tweeters are the same across the entire line, the cross-over design differs to the point where the differences in the highs between the M3, M5 and M100 are clearly audible. The dual tweeters in the M100 may have something to do with it as well. While it sounds like I've knocked the M3, it's not like that at all because they sounded better than my M80v2 in my large space and filled it to boot! I would take them over the M80v2 any day. I had them 12.5 feet apart and I was sitting 12 feet away and the soundstage was amazing. There is nothing wrong with their design like the M3Ti which I had the misfortune of hearing.
The M100s are for the 1% who need it loud and want the ultimate. The M5s are Axiom's gift for the masses who want audiophile-grade speakers for Best Buy prices. Craig Chase is very right to say that M5s with a sealed Axiom sub can go head to head with a $10K pair of speakers. In my living room, I don't even really need a sub with them or the M3 but there is definitely a more tactile feel with a sub (which is why I bought an EP400).
Axiom really needs to be very proud of the entire v4 line and it is a big line for every taste and budget. Who else has that in this industry? As far as I'm concerned, Ian is a living legend.
