I’ll come at it from another angle, (and consider me OFF the deep end on this). Having recently completely replaced a 5.0 with a 6.1. If budget is such that it would allow to add-to over the next year or so. I would budget the majority of the amount towards 2 new mains or fronts and a center. Use your bookshelf in the meantime for the rear surrounds. (and live with an initial 4.0 or 5.0 setup).
My purchase of a 950 sent me (a little lulu) off shoehorning larger speakers into a very small space. (with wicked intents to shoehorn more).
The addition of such a capable prepro made me yearn for better speakers desperately, as the 950 whilst improving the clarity and performance of my original small satellite’s, also highlighted their inherent weaknesses glaringly.

My recent personal experiences are that when listening to 2-channel, - budgeting as much as possible on the mains is highly advantageous. And when I’m listening to HT. You really do still have the majority of the experience centered in that front area with the surrounds adding ambiance. Looking back over what I recently did myself and knowing what I know now about my journey, if I had to budget building a 7.1 up. I would focus on the expenditure across the fronts first. Using whatever hodgepodge fill-in’s for the surrounds I could come up with. If the goal is more enveloping HT I’d then prioritize adding the SW next, (a must for effective HT with smaller speakers and helps with the load many action DVD’s place on your speakers) then turn towards replacing the surrounds in pairs over the next year or so.

One current recommendation for demo for a pair of fronts would be the Vienna Acoustic Bach's. For all around musical satisfaction and excellent rendering of voices very fluid and musical. . I really currently love the sound of the entire line. These speakers (1500 pair at tweeters- and I would get them down 10%) are extremely compact for floorstanders with a very small footprint and narrow cabinet (for smaller rooms) but pack an amazing body of sound for their size. Mozart’s (larger brothers) I do not feel are worth the extra 1K(2500 pair). For the difference in total output to price ratio these are favorite picks of mine at the moment particularly if your listening is divided between categories as you state.

http://www.absolute-sound.com/bach.html

It is fun to come in the door with that new timber matched 5.1 / 6.1 etc. However you go enjoy the hunt!