Tubes for ATC SCM19v2

Don’t bother.  Best you could do is a tube pre with SS amp or a hybrid integrated like Unison Unico, etc.  

Best sound I've heard from the 19v2 was with the ATC P1 amplifier. Makes sense.

The idea maybe frowned upon... but only you can make that decision. I did.
As for my 2 cents and personal experience (1.5yr), I used the ATC-19v2 with the Line Magnetic 805ia. This was in a 15 x 12ish carpeted bedroom. Spaced them a little over 6’ apart. I sat ~8’ back from them. Also, if it means anything to you, I NEVER moved the volume passed the 10 o’clock position. That sound was so tasty sweet you’ll never forget it. Nothing was left on the table. Believe it or not, I was pretty pleased with the bass response. I felt like I was listening to music a lot more then than I am now. I should’ve never have sold them - forum peer pressure. My advice is: If you have a tube amp with the juice, then I’d say go for it! Keep them in good shape because they’ll resale pretty quick. If it works out the way YOU like it, then stay off the forums for a while and enjoy. BTW, you may want to also consider the Triangle Signature Theta for around the same money.

Good Luck!

Thanks for the replies. I am not looking for concert level volumes. My room is untreated at this time. It is 12x19x8. 
What spurred this on was the change in my headphone rig going from SS to tubes with LCD2's.
It might sound crazy but I want to find out.
Thanks