Dan recommends a Mullard 5AR4/GZ34 in place of the stock Sovtek. Sorry, I didn't mean that you should replace it with a completely different tube. However, Dan has mentioned to me that a 5U4G will also work and give a little more of a relaxed sound.
Here is a thread on tube rolling with the LS100:
http://www.audiocircle.com/index.php?topic=92112.0
Here is a thread on tube rolling with the LS100:
http://www.audiocircle.com/index.php?topic=92112.0