I used 600c and changed to 700cx. It was a few years ago, but the cx series i find smoother and a bit darker. If using slighly bright equiptment around 600c it will prove to have a slight sting and perhaps some grain in compairson with cx.
I would go for the cx, no doubt. Even now, using Rowland Continuum, i could gladly use the 700cx or 400cx. Very nice power amps. I think you'll find the cx very nice. The only thing that i did not notice any changes in between c and cx was bass. But in the mid and treble there was obvious changes for the better. Other Krell i owned were KPS 25sc, KPS 28c and KCT.
The KPS 28c was not so much to my liking.
I would really try the cx with Classe CP-65 as i think this was a very nice pre amp.
I would go for the cx, no doubt. Even now, using Rowland Continuum, i could gladly use the 700cx or 400cx. Very nice power amps. I think you'll find the cx very nice. The only thing that i did not notice any changes in between c and cx was bass. But in the mid and treble there was obvious changes for the better. Other Krell i owned were KPS 25sc, KPS 28c and KCT.
The KPS 28c was not so much to my liking.
I would really try the cx with Classe CP-65 as i think this was a very nice pre amp.