SET amp comparable to First Watt SIT 1?

If you want the clarity, quietness, speed of the SIT-1 with superior tonality and spatial presentation in SET, an Audion amp is perfect, and I have to say best.

In your price range you can choose from a simple 300B stereo power amp at $5.5K, up through $18K and any choice would best the SIT-1, by varying degrees. Since you are interested in 300B and alternatives, the DUO is interesting for you at $6K as it can run 2a3, 45 and 300B at your discretion. But you can trust you'll get excellent sound from a 300B, so given your price range, stepping up to the Golden Night monoblocks at $10K/pair is the sweet spot. 10w each amp, all silver wiring, wide-band OPTs. These amps ship with JJ 300B tubes. Put them aside as spares and spring for a pair of KR 300B balloon glass. That will give you high integrity in the bass region where so many 300B amps fail. Midrange tonality, dimensioning and detail are beyond reproach. Top end is extended, spacious, harmonically legitimate and top-to-bottom speed and dynamics are consistent (and *fast*).

There are PSET alternatives, PX25 variants in the line, and 845 monoblocks. If you want plenty of dynamic headroom, the $14K/pr. Black Shadow II 845 SET monoblocks and the $18K/pr Golden Dream 300B PSET monoblocks each output 24 watts. The 845 has a ton of shove but you don't absolutely need it with the Voltis. The 300B PSET Golden Dreams have more power than you need but that amp is musically gorgeous, harmonically complete and full of realistic nuance, so the circuit is worth the overkill.

Phil

213cobra,
Very insightful comments and again another excellent recommendation regarding the Audion line of SET amplification . What do you think of the suggestion above for lncreaed watts via higher power OTL as a perhaps better alternative for the Volti speakers? I believe either path can be sucessful. I’m admittedly personally drawn to the full harmonic qualities and nuance  of well executed SET that you referenced. Many roads lead to Rome.
Charles

Still regret selling my BP amp, his power supply is what really makes them shine. 

We don't have enough info from the OP wrt room size/characteristics and which model Volti he's considering, to answer definitively. Also, I can't find an impedance spec on the Volti site. Nevertheless, I have owned OTL amps and like many of their characteristics, but I've never heard one, especially using massed output tubes, that has the sheer transparency, speed, holistic tone and spatial precision of Audion SET overall, and especially the Golden Dream monoblocks, which would only require a little stretching of the OP's stated budget. I think at ~100db efficiency, 24w with smooth clipping should be plenty, unless the room is cavernous.

I also think at a step-down price of $10K/pair, the Audion Golden Night @10w has most of the qualitative character of the Golden Dream, minus some of the shove. With KR tubes, the bass will gain some discipline. Having recently gotten some experience with the Takatsuki 300B, which is very good, I'll still take the KR balloon glass full range, and it's half the price. Equally well made.

Charles, you know I use Zu speakers at 101db/w/m, and that I've written elsewhere that while such a speaker can clearly be paired with some of the beautiful low-watt 2a3 and 45 offerings, I think they give up too much shove and dynamic fidelity. When 300B is done as well as Audion implements it, and there's a PSET option, why cramp yourself? For shove over ultimate nuance and transparency, the 845 Black Shadow is squarely in the OP's stated economics too, and would put a firmer grip on the very bottom end. But overall, for what the OP seems to be after, he can pretty much index his preferred price to the Audion SET offerings and go, knowing that for the dollar level chosen the march to the Volti will be sublime.

Phil

A bit different recommendation: Audiopax Model 88.

I am coming from an Audio Note Quest Silver and it has everything the Note had plus more. It is capable to show the same midrange magic but has much more versatility because of its power reserves. I am using it with Avantgarde horns where it shouldn't matter, but it does.

It is however a rare find these days (sadly).