Best Speakers with a DNA-1?

Oh, used Treo's are going for about 4,800-5,700 or so and they are rarely on the market. Right now there haven't been any on the market since October 2017.

+1 ctsooner, 
I bought yours.
I'd say that the prices you quote would be for the CT model, and those are as rare as hen's teeth.

If earlier comments are true, the old 2Cs are ‘magical’ — how much more magical can they get?

As has been said before, Mr. V. just keeps adding newer bits and pieces to his speakers, so the closer you come to current production, the closer you are to buying new. The differences are slight, but noticeable.
B

Actually there are none for sale right now.  The prices are for the regular and not the CT.  The only CT I saw that has sold went for around 6k

@ctsooner — I was referring to the Treo, not the Treo CT. Used Treos have selling for ~$3000, which is about what a new pair of Vandy 2Cs would cost. I can also get used 3Sigs for much less than a new pair of 2Cs; wouldn’t both of these options make more sense?

There is no absolute answer there.  It literally depends on what iteration of speaker you are getting.  If you can afford the 3k, I'd probably get a new pair of 2's and a new integrated where you buy them that mates great with them.  As I told you, I'm always a bit Leary getting used speakers.  The Yamaha amp won't give you the magic the the TReo's or any speaker in that range will give you.  It will drive the 3 or lower, but still a new pair of 2's driven by a Rotel, Nad or one of the other integrated amps that AC sells will sound better IMHO.  Funny as I did a search on regular Treo's and noticed selling prices from 3800 (they had scratches on them) to 4500.  None are even on the market right now that I could find and only a couple have been sold in the last year.  Either way, you will get much better sound with 2 to Treo.