Cliff is wrong. We talked about it at the german axe-fx forum and I checked with an analyser, if there is nothing above 11 kHz. Of course there is. The roll-off begins at 16 kHz.
I had some sine waves of 13 kHz and 14 kHz lying around so for the hell of it I reamped them via SPDIF through KPA with only the "amplifier" section active. According to Voxengo Span analyzer they came through nice and clean with hardly any change in the dB level. (Edit: the amp gain has an obvious impact on the dB level of sine waves, with amp gain on zero they did not show anything on the Vozengo Span. I'm out of my league here, better leave it to experts). So it seems that "there is no frequency content above 11 kHz" is not an accurate claim.
But I'm no expert on this and this was with 1.6.0 beta FW. So I really don't know what to make out of all of this. Probably best for me to stop these "science lab" experiments and start playing music. But hey, I got a free hearing test while doing this.