I took a quick look on the web to get an idea for what your current speakers are like -- definitely not the little HTIB system I first imagined
I guess my first questions would be (a) "what do you like and dislike about your current system ?", (b) what is the music / HT usage split ?" and (c) how loud do you play the music anyways ?". It's a pretty safe bet that the Axioms will be more accurate than your JBLs but you already have a very nice system so depending on what you're looking for you could easily spend a lot of $$ on upgrades and not feel that you got your $$ worth.
For anyone else reading the thread, the speakers are :
s-412 mains : 4 way floor-stander with 200w amp powering the 12" woofer
s-center : 3 way center -- 2 x 5.25" at sides plus vertically stacked smaller mid and tweeter in the middle
s-312 surrounds : 3-way floor-standing speakers with 12" woofer
I noticed you have the QS4s as rears and 312s as side surrounds. Have you tried swapping those two, putting QS4s at the sides ? If you're doing mostly HT listening, my first thought would be to put QS8s at the sides (to get the power handling & efficiency), move the 312s to the back, and leave the system alone other than upgrading subs.
If you're listening to a wide range of music (acoustic, vocals etc...) it's not so simple because the Axioms are awfully nice music speakers and you probably would see more of a difference.
For your current room I don't think you need M80s or the extra amp -- M60s and your current receiver would be fine. Spend your $$ on the subs. If your new HT might be noticeably larger or you like to play really loudly then 80s probably are the way to go and you might need the amp (anyone have experience here with a 1500 driving M80s ?).
Personally I would spend $$ on the subs, get some QS8s for the sides and leave everything else as is, at least until your new HT room plans are solidified. For 7.1 music the 312s at the back might be better than the QS4s, but for HT the QS4s will probably be better.
The rest of your proposed system would obviously be really nice as well but I can't say for sure it would be a huge upgrade without knowing more about listening habits & musical tastes.
