The Cambridge Ambience 82s? If so, they are 8ohm and 89dB sensitive... like most bookshelves. They will need a little more power than the more "sensitiv" speakers. I don't know if you're thinking loud or not or what your intentions are. There's also the STR-DE995/S with a little more power... the one I had. (I did run into problems with it driving my 91dB Paradigm eclipses (88dB Anechoic).)
You may want to look at... Onkyo or H/K in that range. Just guessing. I think you already crossed off H/K.
Colby: I haven't heard any in-walls lately. Luckily, I'm single and had a 3,300 sqft. home built here in sunny Orlando Florida all for myself. Don't have to worry about SAF (spousal acceptance factor). <g>
See if you can't take a STR-DE995/S home for a test with your Cambridge Ambiences. You may like it. I don't recall if you said how large your room is? How far you are from the front speakers to your normal listening position? If it's a relatively small room (less than 15' x 15' x 9') this may be a non-issue?
My concern is that in multi-channel mode (Dolby Digital, DTS, Dolby Prologic/II...) you may not get the punch you're looking for with the Sony (lower end line). Since your main speakers (and rears) are in the medium range of efficiency... I'd want to pair them with electronics that will give them what they need -- based on the factors of your room, etc. Then again, you'll probably direct the base cutoff frequency higher (80-100Hz) with those in-walls, so, it may be okay???