The tubes sound great. Best set of EL34's I have ever owned. OK, so it's the only set of 4 I own.
Seriously, I have no reference. I do have some Russian tubes from BSA_79 on Ebay I'm gonna try too. They are about the same price since I bought 8. But unmatched. Anyone near TAMPA,FL want to match mine for a 6 pack (and I'll buy something other than Pabst, unless that's your thing)? I only have an emission tester.
And if I could find a set of RCA 6CA7's to match the two that came with the amp for a decent price, I'd probably get two to try those. I need to look thru my tube box and see what else I have that might work, but I don't think I have more than 1 or 2 of anything unless it's something I specifically bought.
I have a bunch of Tung-Sol 5881's too I might roll, when I get a chance. I know they aren't ideal, but a few people like the sound I hear.
I got my Valve Art's from AES last fall when they offered free matching as well. Seems they do it every 6 months or so. Only on current production tubes, no NOS. AES is a good place. I have bought some stuff here and there over the years and directed a bunch of people there too. Mainly old radio guys, don't know any tube audiophile guys except on the net.
But for the person building their own amp, and not wanting to toast a nice set of tubes, these are great for testing. $44 for a set is less than you pay for one premium tube, and if you start talking NOS Mullards and Telefunkens, forget it.
Oh, and consider the music sampling has been limited to Warren Zevon in my portable CD player on the test "bench", it's really not a test at all. I have a few Telarc CD's that are my favorites for testing. Some of their "Sampler" CD's. And to really test it, I need to hook it to my Polk M10's, which I love, just a personal thing.