Recommend me a tube integrated amplifier

If you are looking for a 300b based amp, check out Feliks Audio.  Brilliant for the price....have enjoyed it greatly with Devore 0/96's.  Full disclosure.....I have one for sale on Agon.  Good luck.

One approach would be to keep your Luxman as the power amp and add a tube pre-amp, like the PrimaLuna EVO 400.

This way you don’t have to worry about driving your speakers yet you have the “tube sound,” which can vary widely but you can have a lot of fun with tube rolling to get the sound you like.

You also don’t have to worry about replacing power tubes nor doing periodic biasing of those tubes.

Finally, if it turns out the tube sound is not what you hope it would be, you can easily revert back to using your Luxman as an integrated amp again.

I have two suggestions, and they are on both ends of the spectrum.

Before my thoughts, I second Cary Audio.  I live about 90 miles from Cary, and I've always been impressed with their gear.  On that note, my first suggestion is to contact Dennis Had, the former Cary guru.  Had makes low numbers of boutique amps and preamps as a hobby now.  I have his LP3.1 Preamp and Inspire 45 Amp pushing a pair of Klipsch Forte II's and it's magical.  You can find used Had gear occasionally.  He recently made a splash with his 300B Amp.

My other suggestion follows what I did when I wanted another well built tube amp, but wanted an Integrated instead of separates.  I didn't want to drop a lot of cash, because it was for a third listening room.  I bought a Reisong A-10 (6 wpc) after seeing multiple reviews, and I was astounded at what I got for $350.  Built like a tank, point to point wiring, tube cage, sounds incredible, etc.  I replaced the cheaper tubes with higher quality tubes from Brent Jessee (so another $500, I got extras) -- so for under $1,000 I have a very affordable giant killer.  Works great with efficient speakers, but I currently have it hooked up to my original Polk Audio Monitor 10 speakers (rated at 89 or 90 dB I believe) and I don't ever go past 11 o'clock on the volume knob.  The Reisong is butter pushing my Klipsch KG 4's, KG 1.5's, and Heresy's.

Reisong makes several other Integrated Amps you should look at.  I honestly call them "Giant Killers" because they go toe-to-toe with amps that are thousands of dollars more.  They are a great amp to "test the waters".  Find out you love tubes and upgrade?  The Reisong is a perfect 2nd system starting place.

I'll second the suggestion of Black Ice Audio.  They're a venerable company (used to be Jolida), they're based in the US and they have very good support.  Their integrated amps have subwoofer outputs.  I haven't heard their Fusion line but a friend has the CD/DAC/Streamer and loves it, and he's a very picky tube guy.

But it's also true that most well-made tube amps will not have an issue with running subs off the speakers taps.

I've thought about the tube preamplifier route, but have read about SET magic on the power side - so I'm going 'whole hog'.