Until very recently I used a VT100 MK3 with my LS25 mk2. This is a very nice combination, the LS25 is an excellent preamp. I have owned an LS2 and my LS25 is in another league it is so much better. When I do upgrade it will be to either a Ref 3 or possibly Ref 5.
BTW the upgrade for the CD7/PH7 power supplies has to do with possible problems from the two 6H30 tubes not aging at the same rate and becoming unmatched. Audio Research did not charge anything for the power supply upgrade for my CD7.