Yeah, my receiver has auto-calibration, so I started from scratch and re-calibrated and that did the trick. Turned out the level of the left channel just had to be raised. Both L&R channels are in the middle of the room (along the long wall of a room, so plenty of room to the left and right of each). But I should have known the right would play louder--for some reason the acoustics in that part of the room make things play louder (and I should have known because the R channel is right next to my subwoofer, which was the best spot for the sub after doing the sub crawl).
I lived with the phantom center (2x Jamo S 803s) for a bit and it was definitely better than using the center channel I had at the time (Jamo S 83). But I just recently got a Hsu CCB-8 for the center and I'm preferring that over the phantom center--even with the timbre issue across the front, it's just a better experience. Not too surprising, I guess--it's just a much better home theater speaker than the Jamos. But I was a bit surprised when my receiver set the CCB-8 at -8.5 db--I knew it was a more powerful speaker, wouldn't have guessed that big of a difference though.