The short answer is no, I don't know a pros pro string to match XP (there might be one).
The longer answer is... I was looking at the Tennisman site in Germany, buying some Discho string, and I was astonished at the range of polys they produce. I wonder if the Iontec process is their way of saying 'Thermo'?
Call me cynical, but I doubt Prince is the only one making a string like XP: I'm certain it will be manufactured by someone else under licence for Prince and I very much doubt they have done anything more than take up an option on technology developed by someone else. As I recall XP is made in Taiwan, but I suspect the technology was developed in Germany.
Good luck! Hopefully someone else will know the answer.