I own a LS5Mk2 and currently have installed Amperex 6922 gold pin White Label PQ which improve over the the standard Sovteks in terms of airiness and the bass is more controlled on my Proac 3.8s. Ive also tried Bugle Boys and like their sound too. I got my PQs off ebay and although they tested great on a military tester they are much noiser than the Sovteks. Placing a Sovtek in V1 & 2 positions has lowered the noise floor greatly. Its easy to get carried away with tube rolling but my personal view is that for the money the standard Sovteks aint half bad.