I'm almost pulling the trigger on a W4S preamp, but want to know if it's gonna be a good match for my Emotiva XPA1's mono amps. I've heard that there's some kind of an issue with the W4S and amps input impedances.
Koestner is right on the money. I have owned the STP-SE for going on 3 years. It is golden with any amp with a input impedance of 8K and above in my experience. I used own a Marsh A400s (balanced input of 4K) horrible match.