I have a gumby (A2) + lyr3 + eikon, and while it's not the auteur, I thought I'd throw some thoughts on this (spoilers: it's a magical combo <3) For the past two weeks I've been using the stock NOS tube that came with the lyr 3, per recommendation from ProfFalkin, which has been doing me well. However, I recently got a little bear b4, was upset that that $80 tube amp actually sounded better (more soundstage, visceral timbre) than the lyr 3 with stock tubes, both out of the gumby. The b4 uses raytheon tubes, so I recently got a Raytheon GTB tube, and I'm happy to say it's a nice step up in terms of slam, soundstage, and clarity. What did I learn? Stock NOS is a good first step (and I do feel it's a step above the other stock tung-sol offering), but I feel it's holding back the lyr 3's potential, and there are better tubes out there, one of them being the Raytheon GTB tube. I also bought a Raytheon VT-231 that's arriving tomorrow, and I'll probably write some impressions on the Lyr 3 tube rolling thread later haha. There's a lot more thoughts in the lyr 3 tube rolling thread, but it's over a hundred pages long at this point... For quick advice, I'd recommend the Raytheon GTB tube I got, which you can get from eBay for around $15 a tube; it's a nice upgrade.