I think adding a seperate amp aside from the amplification provided in the Integra would add considerable sonics. As the power supply in the receiver would be able to dedicate itself to the duties of a pre-amp. And the amp would then become a new issue as what amp to go with. Personally of the 2 you list I would choose the Anthem. But are you looking at 2 channel or 5 channel amps? From what I see the 1552 is a 2 channel amp and the AVM 20 is 5 channel? You might look at used here on AG and see what is available. I saw a Mcintosh MC206 but I think it was about 2500. I saw a few Sherbournes recently in the 1000 range. Sherbourne is a good amp, in case you don't know they are a company of ex-McIntosh folks that build a darn good amp for the money.
There are a number of used multichannel listed.
There are a number of used multichannel listed.