Any merits of getting a Krell FPB 200 C with my existing KRC

I owned the FPB300 amp and it was superior to my older KSA250. I next purchased the FPB600 and it blew away the 300. I spoke with Steven at Krell about updating the 600 to the CAST and he mentioned the CAST has different audio boards that can improve sound without using CAST interconnects, but really improves the sound when used with CAST cabling. Well, I upgraded the 600 and it did indeed sound a little better, but not substantially. I had a good year last year before the market tanked and I dumped the 600 and bought some 650MC's off this site and a demo KPS-25SC playback system. I found some CAST cable interconnects by Transparent for around $300 and I must say, Dan is on to something. The speed, transient attack, dynamics etc. were excellent. I had been using Transparent Reference balance interconnects, but the CAST really gave them a run for their money. The Transparent was better in bass detail than the CAST on my Wilson 5.1's. The CAST was superior in midrange clarity and detail on my setup. I hope it helps. I agree with the others about buying used on this site. You may save some money. By the way, I had a KRC-HR before the KPS-25sc and it's still a fantastic pre.