I heard that 6BG6 valves sounds much better than 6P7S in audio devices and that 6P7S is worthless audio tube, much worse than G-807 and 6P3S ones. At the other hand, I heard that 6P7S has a beautiful clear treble sound, much better than 6P3S. I'm not quite sure - it's just rumours.
As for me, 6P7S is a good choice if you have to put something more powerful than 6P3S (6L6) into the octal socket. Strangely, but 6P7S tubes are rarely used in HAM-radio (compared with G-807 and 6P3S).