I have a very nice condition AU999 which I am using as my main amp at the moment. I have done ALL the mods on the unit and recapped completely including large filter caps. Couldnt have done it without all the info from the great AK'er Sansui heads! I just did the final "mod" as suggested by AK'er Stereofun which was to balance the differential pair of transistors on the driver boards and replace their associated resistors with better matched tight tolerance variety. This has resulted in a noticeable improvement.. quite surprising really! I am not really enjoying my AU999.... But, I have to say I am finding the sound a little fatiguing and the upper mids and highs a little harsh. There is a lot of detail here as well but I find there seems to be an emphasis in that area which is not really pleasant. Just wondering if others have experienced similar with the 999? I should say my speakers are 1970's Tannoy HPD 12 inch drivers in home built 100 liter cabinets. Until recently I was using an AU555A with these speakers which oddly delivers a fatter (maybe less accurate) lower end and none of the harshness in the upper registers.