I just purchased a Simaudio 740P preamp to drive my Pass X250.8 and it is very transparent.
I'm more impressed though with the separation and depth between the instruments. I was not really ready for the latter and it is amazing how live the music now sounds. I've had a Berkeley Alpha II DAC and tried that directly into my amp, but I still prefer the sound I have now with the preamp in the chain. In absolute terms I don't find the high price for the preamp worth it, but in audiophile terms based on what I've spent for the rest of my system, the preamp was definitely worth it.
I've also tried Wyred STPSE, Pass XP10, Hegel P20, and Mystere preamps in my system. I could definitely hear differences between them all; the Wyred and Hegel were excellent for their MSRP.
Good Luck in your search.
I'm more impressed though with the separation and depth between the instruments. I was not really ready for the latter and it is amazing how live the music now sounds. I've had a Berkeley Alpha II DAC and tried that directly into my amp, but I still prefer the sound I have now with the preamp in the chain. In absolute terms I don't find the high price for the preamp worth it, but in audiophile terms based on what I've spent for the rest of my system, the preamp was definitely worth it.
I've also tried Wyred STPSE, Pass XP10, Hegel P20, and Mystere preamps in my system. I could definitely hear differences between them all; the Wyred and Hegel were excellent for their MSRP.
Good Luck in your search.