RAAL is certainly ideal, no doubt. But for $500, you do have the option of a S-2 phantom center, since imaging is no problem. As far as how timbre matching is done? I really wouldn't know, I'm sorry.
But, before purchasing any surrounds, I would give a phantom center a try.
Personally, I was never disappointed with any of the surrounds, I just moved to 2 ch stereo for multiple reasons, as you can probably see.. Less room than before, ext 2 ch DAC, the above reasons, and then some :P