I had the older 250m monoblocks with the KRC-HR pre-amp connected using a balanced (XLR) link and I am now using the 350MCX monoblocks with the KCT pre-amp with the Krell CAST link. My local Krell dealer allowed me to audition the new system at home. The biggest differences in sound I found are as follows (there are technical improvements too but I am not able to describe them).
1. The CAST connection took everything to a better level including more detail, deeper but more focused bass, better separation, just more realism overall. This was confirmed by running the 350s and the KCT with an xlr cable - the difference was not subtle though it is fair to say thre was still a significant improvement from the older combination.
2. The 350MCX monoblocks are less agressive and more rounded even with the extra detail. I confirmed this by doing an ABA test just on the power amps using the xlr cable. If I had done the listening blind I would have sworn that the new amps were not Krell. They did not have the Krell house sound (I am on my third set of Krell amps).
3. On my system, in my listensing room, the extra horsepower and control or grip of the 350s cured a bass boom issue I was getting at the first octave. I am running a pair of Sonus Faber Amatis (which are not power hungry) but this did teach me that there is no such thing as too much power.
Overall, the 350s are better and more powerful amps than the 250s but the most significant improvement was CAST. I was reaching for the cheque book before the audition was over. Hope this helps.
