I owned a Rawson F4 clone. Sound quality was outstanding, but it just didn't work very well with my Zu Druids. With the F4, it's difficult to separate power issues from gain issues. My preamp had 20dB gain and I suspect that wasn't enough, but it's also possible the F4 didn't have enough power. If your preamp's gain is higher than 20 dB and you have relatively high efficiency speakers, it may work great for you.
David
David