I had the Xiangsheng 728A preamp, a Chinese product. Once I worked through a couple of quality control issues, it was a workable tube amp. I didn't notice glaring defects in the sound, nor did I hear any notable excellence from it.
I went to a Van Alstine Transcendence RB 10 tube preamp, around $1000. By comparison, the sound is accurate yet not oversharp like some solid state preamps. All in all, a delight to listen with.