Best used five-channel amp?

I'm looking to upgrade my trusty Primare A30.5 amp to something a little more muscular a higher end.  I have a Classe Sigma-SSP processor and B&W 804s units for the front and an HTM3s for the center.  Does anyone have recommendations for used units?  I've been thinking about the Classe CAV 500 or the Theta Dreadnaught.  I'd like to keep it under $4,500 or so.  Thanks!