Best preamp to go with Mcintosh 501s


I am currently using the C2300 and it sounds great, but I was wondering if anybody has experience pairing the 501s, which I think are wonderful, with other preamps that they find more satisfying than the C2300 or other Mac preamps. I was thinking particularly about the Conrad Johnson Act2, but other recommendations would be appreciated.
ssayeed
I have the MC402 amp and am using it with a Audio Research LS-26 pre amp and am very pleased with the results. I had an opportunity to try a Audio Research REF3 as an in home demo and was extremely pleased. Just waiting till I can afford to upgrade.