I recently purchased a SLI-80 and picked up some Sylvania 6sn7's and Amperex 6dj8's at Tubedepot.com and they sound great. I am using EH KT88's in place of the 6550's. They sound great, but I haven't really rolled the power tubes enough at this point to have a frame of reference. I would like to try some NOS Tung Sol 6550's, but they are pricey.
Good luck!
Good luck!