For $400 to 450+ used how about the Acurus A100X3 ?? For $550 to 600+ there is the A200X3
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Given your parameters you might want to search for McCormack's 3-channel amp(HT3?). It might be a little more than you're looking to spend, but given its smooth performance it may match up very well with your RBHs. If you like it you always have the option later of having Steve McCormack perform one of his famous Revision upgrades, which will make it into a killer of an amp. Best of luck and congrats on the new speakers.
RBH makes great sounding speaks. I am currently trying to decide which pair best suits my needs, after listening to various pairs at my local dealer.
The set you are getting are going to need some serious quality amplification. IMO you will want to bi-amp eventually to get the most out of them (T1&2). I would look for a used, very high current, 4-ohm stable 2-channel initially (adcom would work, used Rotel 1090 would be better) and look to find the highest quality amp you can afford to run the top end in the future.
A freind of mine is ordering the same set (T1&2) and he plans on using a Sunfire 400watt multichannel amp to drive his system with surrounds. Not the best choice economically IMO, but he wants to use only 1 amp and can get great prices because he is a stereo sales rep.
the acurus can't be described as a 'warm' amp, if that's what you're looking for. i've owned both acurus and chiro amps - still have a chiro c-500 - and find it to be a warm, powerful, detailed amp. the c-300 should be available in your range. company out of business, so amps are affordable. great value per dollar.