PSB Image & Marantz AVR
Also, I recall you saying that center channels with dual side-by-side woofers aren't ideal due to combing issues as you move off-axis. Should I still get one of the side-by-side PSB Image center channels, or can I use a third B6 bookshelf speaker as the center channel?
The PSB Image T6 and B6 have a nominal impedance of 8Ω with power-handling capabilities in the 150-200W range, and the Marantz SR5005 can output 100W per channel into 8Ω, so it should have no trouble at all driving the speakers. I have the older Image T65s, C60 center, S50 surrounds, and SubSonic 6i subwoofer in my home system, and I love them. (Like you, my dream speakers are the Revel Ultima2s, but they are far beyond my budget.)
Regarding center-channel speakers, all models with side-by-side woofers have combing issues to one degree or another as you move off-axis. As the distance from each woofer to your head changes, the sound waves coming from them interfere with each other constructively or destructively depending on the wavelength and your position. This problem is lessened somewhat in 3-way designs with a midrange and tweeter oriented vertically between the woofers, because the crossover to the woofers is lower and the range of frequencies they reproduce is narrower, so less of the sound is affected.
If this is so, why are most center-channel speakers designed with side-by-side woofers? Because they need to be horizontal to fit under or over the display. Projection systems with acoustically transparent screens let you place a vertically oriented center speaker behind them, which gets around this problem, but most folks have flat panels, so they need a horizontal center speaker.
The B6 might make a good center speaker if you have room for it under or over the screen (or if you have an acoustically transparent screen, in which case I'd use another T6 for the center). The most important thing is to tonally match the center speaker with the front left and right so pans across the front soundstage are seamless.
Also, if you listen mostly to movie soundtracks, I'd consider using S5 speakers for the surround channels, since they are bipolar and thus create a more diffuse surround soundfield, which is most appropriate for soundtracks. On the other hand, if you listen mostly to multichannel music, the B6 direct radiators would be best.
If you have an A/V question, please send it to firstname.lastname@example.org.