I see that you revived the thread after almost 3 years. Things changed between then and now. I did try a pair of NOS Mazda 12AU7 and loved them for their naturalness and definition in general. I had purchased warranty of 2 years on them and wanted to preserve them. Close to that time, a Psvane representative on this forum mentioned about the new Horizon series tubes, which he said were more neutral compare to the ART series. I had "alright to very good" experience with the Psvane tubes, as you have read my experience above. So I decided to give them a try.
For me, these are so much better than the Art series in every way. I found that they present the music without adding anything to it. I have experienced the "warmth" with the Genalex. But I liked the naturalness of the Mazdas. These fall along the Mazda lines, so much that I did not bother to take the Mazdas out now. Honestly, I like these better than the Mazdas in the bass, there these are a bit more taut. And these are priced at $49 (I paid $55) for the pair, on Amazon. So you really lose nothing and can return them if you did not like them. There are a couple reviews that compare these to the Art Series.
The only concern for me is - how long will these last? I installed them at start of September; so nearly 4 month now. They have been doing their thing and I have not focused on them. I am just happy that they allowed me to enjoy the DAC upgrade very recently. Hope this helps.