Integrated Tube Amps with Subwoofer out?

you should ideally use speaker outs (not pre out) to drive a sub (or better yet a pair of subs)... rel and other firms do this, many (myself included) feel this really helps the sub(s) work and integrate better for hi fidelity stereo sound

Agreed, many subs these days have a “high level” input that is directly connected to the speaker terminals to deliver the signal. As mentioned, REL is one such manufacturer. This method opens your door for many other integrated amps. 

If you do go with speaker level output from the amp to the subwoofer the Raven Audio tube amps have an interesting feature, a pair of speaker outputs with a selectable high-pass crossover at 80Hz or 100Hz that means those bass frequencies are removed from the amplifier section and passed off to the subwoofer, effectively make the amp 2 to 3 times more powerful, according to Raven. My Blackhawk was built before that feature was added so I can’t testify to its effectiveness. When I had an HSU subwoofer the high-level outputs were what were strongly recommended by Dr. Hsu.

+1 on all comments above. I have compared my sub from a pre-out on the preamp to the outs coming via the speaker terminals on the amp. It is far superior when it comes from the speaker terminals. Here's a helpful video (short): https://www.youtube.com/watch?v=bnQOjCuoR9k&ab_channel=RELAcoustics

Raven Audio tube amps 

Thanks for the tip on Raven, it looks like these are made about an hour from where I live and I love that!