which preamp sounds most transparent?

H-Cat 12B with Wavefront Timing Control. Incredible preamplifier.

I am using no-preamp right now (Accuphas cdp directly to CJ amps) - don´t missing my Premier10 a bit.

I would second Soundlock. I have had passive preamps, tube preamps, ss preamps, autoformers, etc. Never have I achieved the transparency I get with the H-Cat.

I just received a custom built K&K Audio TVC that uses S&B transformers. Initial impressions are that it is very transparent and the ability to control the ICs (which can be a problem with other passive designs) is not an issue.

I would recommend that you consider the Placette Active Line Stage, it replaced a ML-32 reference in my system because of its transparent/dynamic/detailed, yet musical sonic signature.