Tube recommendations

6H23 is a Russian tube type but a 6992 can be substituted. These tubes are very revealing and have an extended top-end. 
  With a phonostage it's important to get tubes that are low-noise and tested for microphonics. The 6992 is a tube that can become microphonic.

It seems as though the 
Voskhod 6H23 is a very in-demand tube. I would roll the other tubes and keep this one for now.

https://www.head-fi.org/threads/schiit-lyr-the-tube-rolling-thread.549508/page-559

Excellent comments, @mechans .
Very true about Andy and Brimar, he's knowledgeable and honest, but there are certain tubes he won't sell.    
I placed an order recently and went elsewhere for the Brimar I wanted. Really outstanding tubes.

@infection , Brimars are not as warm as Mullards, that's why I like them. What makes Mullards so special is that adding a premium NOS can make music sound holographic when combined with the right set of tubes. (these are the expensive Mullards).

Brimars have VG high and low-end extension, very natural sounding. I think they are best when used in the preamp line stage or as input tubes in an amp.
These added some warmth to my system without rolling off the highs...
https://www.upscaleaudio.com/collections/preamp-tubes/products/brimar-cv4003-12au7

The 12AX7 Brimar goes for about $120 to $150 each. But the best is a CV military type for about $150.