surround speakers to match Meridian P350W

I have a Meridian G68 processor, a G57 amplifier and a G55 amplifier, which will suffice to drive a 7 channel surround system. I started with buying 2 Meridian P350W (wall mount speakers) for stereo. Now I am looking to add a center, sub, rears and sides. Of course, I could add additional Meridian speakers. But other than Meridian speakers, what else would be a good match? I want the best possible sound for stereo and have spent the money accordingly. But I haven't heard much difference between expensive and less expensive speakers for a surround system. What would be a good solution?