The Kappa series and the RSB series were designed with tube equipment in mind.The medal tweeters are very hot and require power that is rolled off. I have a pair of RSB 3b's and I used to use a modified Adcom 555 with much success but the original 555 is not a good match with these speakers. I would go on Ebay and either look for a Hafler DH 500 which has MOSFET's or buy a Carver amp with 200 a side which is what I use on my Infinty' in my second system.