Gte57s,
I have been using an L1 for the past 3 years and currently have the 6h23neb tubes installed and they sound fine to me. I have had them installed for about a year. Before that, when I bought my L1 it came with RCA brand 6DJ8 tubes (made in Germany)which were supposedly made by Siemens in the 60's or 70's. I changed them after 2 years of listening (a lot)just to try something different. I really can't say one is better than the other but they both sound great to me.
Some people on these forums like to indicate that any and all preamps made by AI eat tubes. In my case I certainly haven't found that to be the case so yours may be like mine and not go through tubes.
When you say the sound is dry, I'm surprised no one asked what source, amplifier, and speakers you were using as this could make a lot of difference. One thing about the AI preamps that is different from many others is the fact that they are phase inverting. This means (according to the AI owners manual)that you should switch the red and black speaker cables at your speakers so the red cable is connected to black speaker connector and the black cable is connected to the red speaker connector. Doing this may help but only do it with everything turned off so you don't inadvertantly touch them together and damage you amplifier.
I assume you don't have an owners manual for your preamp. I bought one from AI after I bought my L1 and it took F O R E V E R to get it. If you would like a copy, send me an e-mail with your mailing address and I will send you a copy. It's pretty simple and may help answer some of your questions.
Good Luck.
Al