Bite the bullet and find a nice pair of Amperex USN or USN-CEP 6922/7308s, from the 50's or early 60's.
They're not all that salty!
If you can mix one with a Siemens in each channel; you'll experience the warmth you seek, without any soupiness, or blocking of the air/clarity you enjoy from the E88CC/CCa.
Been there/done that*
They were supposedly built for quiet operation, but: destined for a preamp, I'd be certain they're tested for noise anyway.
The Russian Rocket tubes were supposed be dazzlers, but: good luck finding the rare, good years at anything reasonable.
I'd just be surprised if you can secure something currently in production, that doesn't sully the sound of your Siemens/system.
*ditto: Duelunds, etc