I'm no Guru, but like you said, the in-walls probably won't be in the same league as your tried and true bookshelf speakers.  But, they should capably serve your purpose of striking a balance between WAF and quality sound.  You have a good sized room, so I suggest swapping out the 6-IW with a 6-LCR for your center (unless you don't want to deal with cutting a stud, or your tv is fairly close to your couch).

I suggest selling this to your wife as you're willing to compromise on the in-wall speakers as long as she is willing to let you replace your sub.  Then throw out the 10-incher and get yourself something killer (for what it's worth, my wife is an interior designer, and she allowed me to squeeze dual SVS PC13-Ultras behind my 6Ts).  Seriously, you have a good-sized room and could likely benefit from a larger sub (or two).

I use a pair of Aperion in-ceiling speakers as my side surrounds and they are fine speakers.  Assuming I eventually get a pre-pro that has Pro Logic IIz, I will likely add a pair of 6-IWs for the height channels.  I haven't heard wides or heights yet, but from what I've read, it sounds like they benefit movies more than music (personally, I'm a 2-channel stereo guy when it comes to music).  At any rate, I know you'd be happier with in-walls all the way around than nothing at all.  So pull your head above the water and let Aperion show you the way.

-Nick