Best I can tell, the Acurus/Mondial amps are a slightly colored / slightly liquid type of sonic signature - much like the liquid/lush cleaner type "Class A" amps, such as the older Krell (or new Krell iBias) or even a little like Levinson (though, not nearly as liquidy sounding as Mark Levinson is). If this is the sound you're after, you could give it a try, but I suspect the warm sounding Marantz may create somewhat of a mush/mess with this amp. If you got a very clean HT processor, such as the Anthem, then the Acurus might have been an interesting "coloration" on the sound. The Acurus is not completely clean/clear when compared to other amps. I would take that "200 hours" with a huge grain of salt! lol.
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The Rotel amplifiers are going to sound a lot cleaner and clearer and they mate well with the B&W speakers. There is an Emotiva XPA-5 "Gen 1" on audiogon for $699 OBO. The Emotiva is a very fast amp, but if you load it with Furutech fuses, it sounds quite good. It may be a good match between Marantz processor and B&W speakers.
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There is a Rotel RMB-1582 for $699. It's only stereo, but you could start with that and then look for another good resolution 3-channel amp.
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Just ideas.