As Gmorris noted, I am also in no hurry to upgrade to the latest ARC versions of the LS25 and VT100. The LS25MKI is a really nice preamp. Prior to the LS25, I owned a demo late-model Ref1. Sonically, both were very similar, with the Ref1 edging the LS25 out in soundstaging. Because they were so close sonically, I sold the Ref1, bought a used LS25, and pocketed the $difference. Regarding tubes, I have had really good success with Amperex 7308's, Siemens 7308's, Tungsram 6922's, and Mullard 6922's. Currently I am using a pair of Tungsrams and a pair of Siemens to good effect. This preamp really allows you to hear the improvements by using one 3mm Marigo white dot place at the base of each tube between the pins...much more air, blacker, more palpable mids. I know of no better cost-effectve tweak than the Marigo dots. I also found a nice improvement in performance by replacing a Synergistics Research Reference Master Coupler with a Harmonic Tech power cord.