Proceed AVP or Meridian 561?

Hello all. I'm new here and am going to start building an HT system. Currently have no surround processor and am intrigued by the above 2 units. Hoping to pick one up used. I also have an old Bryston 3B amp and .5B preamp running a pair of NHT 2.5's. Where do I start? Use the 3B? Buy a new 5 channel amp? Any comments will be greatly appreciated.