Greetings, all.
I have indeed had some nice preamps in the past, several of which I would dearly love to have now to try with my LM 508. Alas, they are long gone. I have been running my 508 strictly as an integrated since I bought it and have been so pleased with the results (after tube rolling), that my incentive to shell out another $3-5K for a preamp has been fairly low. Then again, I am a big believer that a high quality preamp can and would add another dimension to the sound.
I do not doubt at all that radiohead99's observations are spot on. One of these days, I'll find a good deal on a preamp and try it out. In your price range, you might find a Don Sachs Model 2 come up at some point, or one of the cheaper Backerts. Those are two I'd like to hear with the 508.
I have an Allnic phono stage that I like a lot, so I bet radiohead99 is getting great results with the L300o Mk2.