David, fair question...I tried a few different pre-amps in the combos, all with the same results to me. I settled on a little known bespoke pre-amp called the Truth from the Horn Shoppe...an insane steal at like $1200. It has no amplification (so low-output phono pre's may struggle--mine is good), but is powered and is buffered (so not a passive either). I was skeptical when I bought it a few years ago, but it's easily bested both the Audio Research LS-28 I demoed for a few days a couple of months ago, and also beat my Marantz SC-7S2 reference pre-amp (no longer made, but $6500 when new--since sold). The Truth and Marantz are solid state, and the LS-28 is hybrid, I guess technically. So to your question, I never got my hands on a fully-tubed pre-amp of any quality--it's possible that may have made a better pairing with the SIT-2 for my tastes. The Zu guys reportedly love the SIT-1s, so I'm being super nit-picky when I say that I didn't prefer the SIT-2 over the PL HP with any of those pre-amps. It's very, very close.
To be sure I was being fair, after posting above, I actually immediately put the SIT-2 back into the system for a day and listened for about 2-3 hours with it. I confirmed my feelings one more time.
To be sure I was being fair, after posting above, I actually immediately put the SIT-2 back into the system for a day and listened for about 2-3 hours with it. I confirmed my feelings one more time.