B&K - I had a B&K 7200 a long time ago. It was a very nice amp, very powerful. However, in the end, it was just too warm sounding for me. Nice amp, though, if you like the warm sound.
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Sunfire Cinema Grand - I also had one of these. The sound was pretty good, but ultimately it wasn't that interesting/exciting. Good resolution, but the circuit was much like a class d circuit (patented downconverter). It sounded rather boring. Others have different opinions.
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Classe - the older Classe Audio amps and equipment were a LOT warmer sounding than the new stuff. Nice, but warm, lol.
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Parasound HCA and Classic - these are lesser refined versions of the Halo A21 stuff. Very good for the money and can pack a lot of power. Parasound is on the slightly warm side of neutral, but not as warm as B&K. However, pairing warm Parasound with the warm Marantz may lose too much resolution.
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Bryston - this is the one amp out of the list that is different from the rest, lol. Bryston is extremely fast and high resolution. The older first generation stuff was somewhat dull sounding, but they got better and better as time went on. The SST2 version is probably the oldest I would buy right now. It is very fast and high resolution, but I think it was a little sterile. Not bad at all. It might work out very well with the stock Marantz processor (without the fuse upgrade). You could try the Bryston amp and do a Furutech fuse upgrade internally - that might make it sing better. The Bryston is likely a little faster and much more refined than the Emotiva XPA amp. I've heard people who had Marantz processor with a Bryston amp and they were very happy.