The speakers you have listed retail for $3,145. Add two reasonably-priced subs (e.g. the Hsu VTF-3MK4 (12") for $1,319), and your total wil be ~$4,500. Consider several alternatives:
Substitute 2 x Image B6 for the 2 x Image T6 fronts, and upgrade to dual Hsu VTF-15H (15" vs. 12") for a total of $4,105.
Eliminate 2 x Image B6 rear surrounds, keep the 2 x T6 fronts, and upgrade to dual Hsu VTF-15H (15" vs. 12") for a total of $4,305.
If your objective is high-quality home theater sound with immersive bass, your budget is better spent on the best subs you can afford (two, of course). The Image B6 bookshelf speaker has the same mid-range and tweeter that the T6 has, and since you will be re-directing the bass below ~80Hz to the subs, you won't hear a difference between the B6's and the T6's for your front speakers. As for the rear surrounds, keep in mind that only a small number of movies are actually released with 7.1 sound tracks. For all other 5.1 sources, the only thing you hear from the rear surrounds are synthesized sounds, e.g. PLIIx Cinema. If you look at the Audyssey recommendation, your speaker dollar is better spent in the following order: First DSX Wide speakers, then DSX Height speakers, and lastly surround back speakers. BTW, what AVR do you have? Does it support DSX?
If you eliminate the rear surrounds and try the B6's as the front speakers, you can always move the B6's to the rear surrounds and purchase T6's for the front later. This way you can evaluate the sound and make an informed decision down the road.
Edit: You do not want the S5 as a rear surround.