consensus on passive preamps?

I recently located a Carver Lightstar Direct passive pre to
match my Carver Lightstar Reference Amp. With the two stable-mates together, I was expecting miracles. The tranparency was immaculate but the overall sound was thin. I would welcome any suggestions that would help make the sound fuller and richer.

I agree with Glreno, that transformer-based passive attenuators are the way to go. I'm using a DIY Bent Audio TX102, which should be very similar to the Silver Rock (I'd like to know how they actually compare), except that it's a bit more versatile and not quite as expensive.
What I want to point out is, that transformer-based passives don't have any of the drawbacks (impedance matching, requirement for short interconnects) of the resitor-based units and as such they are IHMO the best thing since sliced bread.

Can't imagine trying to drive my Aleph monos without their Aleph P!

Best for more than one source component: a remote-controlled passive attenuator (stepped/potentiometer or even transformers) next to the power-amp inputs... = negligible cable influence.

...and to meet the topic: I can't imagine a better pre-«amp» than a passive one. Possibly a transformer design sounds best of all. (I have a 10-kOhm Alps potentiometer.)