An important factor for the 705 is the
pre outs for future power amps (I have always griped about why Onkyo's pre-out capable models have to start with the 7 series) The more power the better!
If this is not true, why is a 50w subwoofer "bitin"?
IMHO, I also observed that the higher the models the more musical they are, as the receiver engineer/designer has more budget for better parts. And this is true not just for the power section, but for the
pre-amp as well.
A practical suggestion I can give you for your audio preference is:
Onkyo 705 + a decent 5.1 satellite (or entry level bookshelf) speakers system for your HT, then a good mid level FS for audio connected to your Onkyo's
speaker B. This way you can change your audio speakers from time to time w/o worrying about the center & surrounds. I believe this option is cheaper than going for all 5-7 mid level speakers.
A good CDp is a must, then maybe a power amp in the future.
If you like harder to drive speakers like Dynaudio for your music, go for the 805, as its THX ultra and their amp sections are torture tested to 3.2 ohms before they pass the THX ultra certification.