Audio Research LS2B mk2 cap ugrade

The voltage rating isn't an issue. The voltage is a maximum rating; as long as you operate the caps at less than the maximum, you're ok. The highest voltage in the LS2 is around 425v. A cap rated at 450v or above will do fine.

I still think you will get the most bang for the investment out of a pair of 1uf V-Caps on the output. Beyond that, I would be thinking about replacing the preamp with something else. By the way, I would also recommend using the V-Caps without a small bypass cap. That's what the V-Cap mfr recommends, and I prefer them that way in my own equipment.

The input, I think if it follows suit with the rest of Classe amps because Classe does not list the manual and without sending a email to Classe, the 100-101 and 200-201 are 75 kohms while the 300-301 and 400-401 are 16 kohms.

I have also used AR LS9 with it with a Krell Showcase DVD, that was a nice combo but I did not like the stepped volume on the LS9 as it did not have enough steps.