Audio Research LS-22: Best Tubes for this preamp?

Your best bet is to talk to Kevin Deal at Upscale Audio in Upland CA. He's the "tube-guru", and should have the best aadvice...from my experiences anyway. Infact, if you put a post up asking people's oppinion on Kevin's advice, I think you'll find favorable results.
Good luck

Have you read this in-depth review of 6DJ8/6922/7308 tubes in Audio Asylum's FAQ section:
http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html

Well it doesn't answer your question directly, but will give you a broad overview of each tube's strength and weakness. I've tried most of them on my ARC LS-2B mk II, and I agree with most of Joe's assessments. My favorite is the Mullard Master Series 10M 6DJ8 which is not reviewed by Joe. This tube is very rare. I was just lucky to find one at a local electronic store. When it dies, I will be replacing it with my second and third favorites: Amperex 7308 whitle labels, and Amperex 6DJ8 orange globe lable.

FrankC

In my ARC LS15, I noticed a dramatic improvement in imaging, transparency and subtle inner detail when I replaced the four Sovtek 6922s with a pair of Siemens 7308/E188CC and a pair of German made Amperex 6DJ8 orange globes. Any of the Amperex 6922 PQs will sub nicely for the rare German Amperex.