Is the Marantz PM8006 powerful enough to power my B&W 802 Matrix Series 3?

It is probably "sufficient", but those speakers like more power.

What would you recommend around $1000 or below used on ebay?

Umm, you are not going to get a Yamaha A-S2100 used for under $1000 unless some dude’s angry ex-wife sold it to you.

Try the A-S801, it’s voicing will also try and remedy your B&W’s brightness. Beware of a lot of amps with your speaker unless your ears love/were forged in the flames of brightness.

https://www.crutchfield.com/p_022AS801S/Yamaha-A-S801-Silver.html

Thanks soooo much!!!