$1000 used amp. What can I buy?

Give the McCormack amps with revisions a try. They are rarely sold for very good reasons, one of which is they sound superb. You may also look into some of the digital amps like PS Audio's HCA-2, quiet, runs very cool & load invarient.

I definitely like your suggestions.

WIth every system I have owned it has benefited from splitting the low frequencies from the main speakers. That might not be the case with large speakers that have dedicated cabinets for the low end drivers, but those are usually recommended to be biamped as well. But we are now talking much more money than most of us can spend. The midrange seems to open up with the bass being ran through a separate driver and amp. Getting rid of the low frequency caused distortion of the woofer allows lower distortion in the midrange. Also this lowers the power requirements to drive the main speakers. The down side is that you are adding another part(external crossover) that can degrade the signal and parts must be of high quality.

Musical Fidelity A3, A3.2. Dual mono design, very nice