Old or new gear

I would look at Atma-Sphere amps. They are built very well and give excellent sound. A used S-60 or M-60 should be in your budget. I would call Ralph at Atma-Sphere, he sometimes has demos and units for sale at a significant discount (that's how I got my MA-1's).
He can also give you advice on what will work well with your speakers.
Bob

With your speakers and practice of listening at lower levels in a small room, you should have many choices and alot of fun ahead. Additionally, if you went with a fine integrated you wouldn't have to worry about matching the pre to the amp let alone the cable nervosa certain to strike. Some nice tube integrateds that are reasonably available pre-owned that would fit the criteria you gave regarding countries of origin: Cary SLI-80 F1, VAC Avatar, Leben CS300-XS, Audio Research VSI-60 immediately come to mind. Service is convenient and reliable and they would each comfortably mate with your speakers. Also, within your budget you could spend a few dollars on a dac that would potentially be more musically pleasing than the Behringer but YMMV.

Disclaimer, I am not a dealer but have I have owned alot of tube integrated through the years and have loved the synergies of each for different reasons with different speakers. The Cary is nice with a nice headphone section, remote, easy to change the flavors with all of the tubes on board. The Avatar I simply love. No headphone but the original el34 based unit is magical. Some had remote, some didn't, just ask the seller which one. Over the years, it evolved in search of more and more power to the kt88 and lost a bit of its graciousness IMO. The original Avatar was the evolution of the Matantz 8b reissues VAC built and the Avatar I have always considered to be the *b integrated that Marantz should have built but only VAC and Kevin Hayes could achieve. I have owned 3 of these (have one now in my 3rd system and may or may not part with it. its perfect condition and they are hard to find in perfect condition) and keep coming back. Killer phono stage, no headphone, VAC service is A+++ should it ever be necessary. The Leben, within its power limits, is amazing. I have owned 3 of them as well (have one now in my office). Nice energetic amp and punches way above its 15wpc rating. Bass boost and great headphone but no remote. The Audio Research is a very nice amp, especially for what they sell for used. Not as "tubey" as the 3 prior amps which for your purposes may or may not be a good thing. I presently have a GSI-75 in my main setup and I LOVE it. Audio Research service is terrific. Others I have owned but will not again: McIntosh 2275 tube integrated, Line Magnetic anything, I've had 2 I purchased pre-owned and I always felt I was on some strange drug that made everything happen in slow motion when listening to the LM Audio amps LOL. I've had a few ss Macs which were fine and solidly built, a Nagra integrated which was excellent but a letdown for the $ spent, a BAT 300xse which was a fine hybrid.

You have alot of options but I've always liked buying with the peace of mind that a strong service oriented company is there when you need them. McIntosh, Audio Research, VAC are terrific in this regard. BAT probably is Ive just never needed service for a BAT. Cary Audio may be different now that Dennis Had retired so I don't know. Leben and Line Magnetic is through Tone imports so I'm sure its probably terrific although if you buy used it might be tricky, especially if you accidentally bought something gray market. My Lebens have been rock solid. I would be very surprised if the Schiit pre is a perfect match with all of the amps you are considering and great 6sn7's are not cheap. Probably TMI. Good luck!

Thanks. What are some other alternatives for preamp (SS or tube), under 1K, that would match fairly well with many different types of tube amps, if there is such a thing?

Pick your amp and then pick your pre, or vice versa. Impedence matching matters. Thats why you may read that someone has a dac with a volume control that works perfectly feeding their amps direct sans pre, while others proclaim their system collapsed. They got lucky that the dac matched up well in the volume range they listen with the amps they chose. There is alot of data out there but it adds another layer of complexity to chase down in the event you are not thrilled.

@sophie999, I think your inquiry about Quicksilver monos is a great place to begin, and end...

I just sold my pair, as I'm moving to a house half the size of my current one.  Both love and respect the build and sonics of the Quicksilvers, along with the fact they're made in America.  You can't go wrong with them, as they have an incredibly simple (Dynaco), hardwired circuit.  Outside of blowing a transformer, no matter what ever goes wrong with them, you can easily source replacement parts, and either make the repair yourself or have a tech do so.

I also second the Dynaco suggestion from @roberjerman.  Obviously, what I said about Quicksilver holds true for Dynaco.  Given the company produced several hundred thousand amplifier kits, the vast majority assembled by folks with zero electronic assembly experience, it seems easy to say Dynaco produced the most reliable high-end audio components of all time.  Most underrate how good they actually sound, however.  And in my opinion, having heard most of the modifications that "fix the design flaws", I believe the original sounds (and works) best.

In my opinion, a simple tube design, whether SET / PSE or push-pull, employing hardwired construction represents the best long-term purchase when it comes to amplification.  Such products mean you'll likely never get stuck someday owing a mega priced doorstop.

For what it's worth, I previously served as the North American importer for Opera Audio / Consonance.  The company builds a staggering array of products, including tube amplifiers, specifically.  Some of the tube amplifiers sound really good.  If I would recommend anything they produce, they would lead that list.  That said, many had the sort of implementation and reliability issues that go with 1) building so many products that none receive the level of attention in terms of design, implementation, support, and iterative improvement as a company dedicated to building tube amplification alone, and 2) the gap between the owner / designer of the company and the folks actually building the product.  Given most employ printed circuit board construction, over the long term, I would have reliability concerns not present in the aforementioned two products