Are there any smaller Advents like the large ones you are restoring? If so, that's what I would suggest for the center channel. Better yet to get one just like the pair you are restoring. If you can't find a center speaker that's voiced just like the left and right speakers, or if they're just too large, then I would prefer a phantom center.As for the surrounds, I would prefer them to be somewhat similar, or at least they shouldn't stand out. But they can be different speakers. Some full range or mini-monitor speakers would be just fine for surrounds.