In what department you find roxanne is better than JH13 FP? JH13 FP for me is more tonal accurate. It has more neutral mid presentation and linear treble that extends way further than roxanne. JH13 has more micro detail, and transparency. The soundstage width is about the same size as roxanne. The roxanne does have a more sense of depth. JH13 FP presents clarity with better balanced/combined resolution and brightness. In contrast, roxanne has a peak at 7-8 K and then roll off pretty badly, so although it does sound like it has greater instant clarity/detail because of the lifted brightness, it can make some songs sound harsh/sibilant and lack of transparency. Increasing the bass does help, but then it make the mid and treble sound more dull. Roxanne has better bass than JH13 for me because I am a hip hop fan and I am a fan of good quality of bass, but some people might not like the bass gain.
JH16 FP on the other hand, doesn't have as extended treble as JH13. I prefer it over roxanne because the mid is not recessed to the extent of roxanne's. Without bass, the frequency response of roxanne sounds so like the old verison of JH16.
I will have to wait for the custom version of my K10 too. The demo I auditioned have similar technical ability of JH13 but with a more accurate and neutral tuning to my ears.