I have the Arcam P85/3 driving centre and rears in a 5.1 system. It matches the A85 (which I'm currently using as a power amp only at the moment).
I think it's very good, certainly excellent value for money at £250/channel. I don't exactly think 'wow, listen to the amplification of the rears' but as it's the same power stage as the A85 and I loved the improvement this bought to my stereo sound, I'd say it would be a great choice. No experience of TAG (well not power amps!) though.
I guess you would need 2 x 2-ch P85? I think they're about £500 each.