RC, welcome. As to your "musicality" requirement, there's no reason for concern on that point about either of the receivers that you're considering or any any other competently-designed modern unit. Operated within their designed power limits(essentially identical)they'll amplify transparently without adding any audible sonic coloration of their own. You yourself can change this with tone controls, ambience processing, etc. when you want to.
If you're willing to reposition the "office" speakers for surround duty in the "theater", as you mention, that'll certainly help with the budget, but for side surrounds in a 5.1 HT setup the QSs are really excellent because of their very wide dispersion. If you can budget for them it's suggested that you'll get more enjoyment than using either M2s or M3s as side surrounds. If eventually you expand to a 7.1 HT setup, the M2s should be fine for back surround speakers to lend a more specific localization of back effects, but QSs also work well back there, of course.
On the sub, regardless of how big and powerful it is, you're in control of how loud you set it, and any sub can obviously be made almost inaudible. You of course would be wasting the capabilities of a very powerful sub to do so, and apparently you want to economize in that area. If you could go a little higher into the $200-$300 range, there are subs from sources such as Hsu which might satisfy you more.
