Need to learn about Audio Research

You should keep the H390 and add a Tube Preamp and/or even a Tube DAC like Primaluna. You’re not going to get better for less than $10K than the Hegel. 

Look at the Rogue Audio Cronus Dark. All tubes. Beautiful sound and build. Made in PA so easy to get parts and repaired. 100wpc. If your speakers are not hard to drive, this would be a great choice. Sorry didn’t see the SS requirement. 

I attended the Southwest Audiofest in Dallas this weekend and visited the Audio Research room.  They are releasing some new products in a couple of months.  I don't recall all of them but there will be two solid state amps, a couple of tube amps and I think a new integrated amp.  I think all of these will be at the "lower" end of their price range of products.  I still own a the LS-15 line stage which is nearly 30 years old.  I had it modified/upgraded about 10 years ago and it is still sounding sweet.  I am curious about one of their newer SS amps.  I also owned their 100.2 power amp a number of years ago but regrettably sold it.  I've been impressed with the quality of their products and customer service.

You should keep the H390 and add a Tube Preamp and/or even a Tube DAC like Primaluna. You’re not going to get better for less than $10K than the Hegel. 

I have a tube DAC, Lampizator Amber 3. 

Seems that adding a preamp to an integrated would be knda silly.
 

I don't think 100 watts of tube or SS power is going to cut it with 3.7s. I'd be looking for at least a high current 200 wpc amp.