Can't say I know anything about the sony amps, the Adcom mono's are pretty old, I would check with Adcom and see if service can still be had on them. They got a good review in stereophile years ago, class B if I recall. Aragon 4004 can be had in your price range, Belles 150a hot rod is for sale on audiogon also. I don't know the output of your sony, you will need to factor that in your choice of amp if you are going to go without a pre-amp, your speakers at 84db could be a problem in passive also.