I had a Proceed AMP 5 that I paired with an Integra DTC-9.8 processor and thought it was a fantastic amp. It may be psychoacoustics based on what some people on this forum say about all amps sounding the same, but to my ears, I thought it sounded better than the Sunfire Cinema Grand and NHT Power^5 IcePower amps I was able to compare it to when driving my Vandersteen 3A Signature speakers.
Never had a chance to compare it to a Bryston, Classe, and other high-end amps that the Proceed is often times compared to. But considering it retailed for nearly $5000 new and now can be had for <$1,300 used, I think there definitely are some deals to be had on the AMP 5. Good luck trying to find a used Bryston 9BST at that price.
Just be forewarned that the Proceed AMP 5 is large (20" deep) and heavy (~115 lbs.) so make sure that your rack can accommodate this beast of an amp.
What speakers do you have? Based on what I hear about the quality of the amp section in the Anthem MRX, might be worthwhile trying out the receiver first before jumping to the conclusion that the amp section is inadequate and buying an external amp needlessly....