I'm very pleased so far with your Xenon limiter. I was thrilled to get something which adheres to Bob Katz's K-system. I suggest one feature. Near the end of his article How To Make Better Recordings In The 21st Century Katz states that one might get improved accuracy in certain situations if narrow-band pink noise is used, instead of full.

You could make the three calibration noise settings available at full and at narrow-band as well; he specifies 500-2kHz, RMS -20dBFS. I've been generating it myself, but it would be nice to just dial it in right there in Xenon. Thank you!