Pure Class-A Amp under $2000 (USED)

FWIW...there is a First Watt M2 available right now for $1850. It will work well with 6-ohm speakers. Your sensitivity at 88dB is lower than I would like but you will get decent sound as long as you don't expect to rock the house. I have an F6 controlled by an NAD C658 connected to Focal Kanta No.2 speakers rated at 91dB efficiency and frankly they sound great and can put out enough volume to drive the wife out but I like MORE so I just ordered a set of Tekton DI's rated at 98dB efficiency. 

My 2 cents

Used First Watt M2 for Sale | HifiShark.com

+1 Schiit Aegir(s) x2 monoblocks.

I currently run a pair of Schiit Aegirs into my Wilson Benesch speakers which are, I believe a 6 ohm speaker with no difficulty at all, 80 watts per monoblock and I never have it over 25%. Lovely sounding class A, first 10 watts are pure class A, balance of the wattage is something called class A "continuity". You will have to check with the website to get the details, listed as Class A in Sterephile. I beleive they cost me $ 2,500.00 new delivered in Canada so you should find a pair used well within your budget. 

+3 Schiit Aegir, I have one it drives my speakers with finesse in stereo mode. 😎

Mike

+4 on the Aegir. I have one in my main system for my 88 dB 6 ohm Ohm 1000 speakers and it easily goes to my loudest needed volume (about 85 dB average) without strain. (Full disclosure, I also use a sub.)  And, I love the sound -- previously had a Bel Canto amp and then a VTV Hypex that were both higher wattage but didn't sound as good. 

Schiit offers a 15 days trial with a 5% restocking fee if you try and don't like. $40 to try it out (plus returning shipping) which is a pretty good deal. And, there is also a solid used market for Schiit gear -- you can use it for a year or two and not be out all that much if you choose later to move on.

There’s a minty looking Krell KSA 200 on Audiomart @ $2100