Krell x-series, are ther any sonic benifits?

I would tend to agree with Ericbee - Krell did it probably for marketing purpose. Looking at the specifications the entire new line of amp have the same weights and dimensions as their predecessors, yet they are each 100W more powerful. Since the size of the heak sink stays the same, one may assume that the number of power transistors also remain the same. So how do they squeeze the extra power out ? Perhaps by adjusting the operating region ? The amp may sound better than the replaced version but I suspect the improvement may be subtle. As always, the only way to find out is to do a side-by-side comparison. Has anyone done that yet ?

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