What is the best USED Speaker Under $10,000

I second the earlier mentions of the Legacy Whisper and Revel Salon 2's. I would think you would be struggling however to find a pair of Magico S3's for under $10k any time soon. Infinity IRS Beta's can be found in good shape for under $10k used, but their age and lack of replacement parts precludes me from recommending them.

Personally I vote for TSW Apogee Duetta Signatures which offer remarkable sound for the money, whilst in a smaller room or where less critical speaker placement is required, I vote for the [url=http://app.audiogon.com/listings/full-range-marten-design-coltrane-alto-low-hours-excellent-condition-2014-12-13-speakers-92868-orange-ca]Marten Coltrane Alto's[/url] on A'gon at the moment. They were $22k speakers back in 2004, and even at that price Marten weren't really making any money on them due to their extremely complex design and carbon/kevlar monocoque construction.

Another speaker that represents excellent 2nd hand value is the Living Voice OBX-RW which can be had under $10k used.

I heard the B&W 802D's in a treated room with Electrompaniet amps and preferred even my old classic Infinity Renaissance 90's. I've never liked B&W's diamond tweeter which I find fatiguing. I would think the TSW Apogee Duetta Signatures, Living Voice OBX-RW or the Marten Coltrane Alto's up for sale on the 'Gon would sound more musical.