Krell x-series, are ther any sonic benifits?

Side-by-side comparison for an individual would be difficult. I personally don't know of anyone who has a pair of FPB amps... However, I sent my 600c for the upgrade. Time will tell. Although I won't have the opportunity to compare side-by-side of before and after the upgrade, I usually hear the biggest differences in audio gear when I first insert it into my audio chain. So, I will report when I hear it.

Kichoi, please keep us informed. I would be keen to find out what improvement a $500 upgrade offers. BTW, do you use the KCT preamp ? If so, does Krell provide any upgrade to CAST II for it ?

Actually the 600C upgrade to 700Cx would cost whopping $2000... According to Krell, it will operate exactly the same as the new 700cx once the upgrade is done. It will have minor cosmetic changes; one on the face plate to make it identical to the new onces and a new sticker with 700cx ID for the back.
I have not asked them about the CAST II. I will do so.

In case I forget, please send me a note in couple of weeks. The amp is scheduled to be back in 1.5 week.

ericbee: great point but being such a large company like they are in regards to sales because they arent a big company in general. I would think that they would stand to lose many loyal customers if the upgrade was a small change in sonic quality. I sold the krell and went back to Levinson

Actually the upgrades will cost $500 per chassis if the units were bought October of last year or later, $1000 per chassis if bought earlier and $2000 if the amps was bought used or from an unauthorized dealer.