Why do preamps improve sound of CDP?

Looking at my post I should have emphasized how much this is a matter of taste and associated equipment. Before I purchased a Transparent Reference digital cable I was using a Musical Fidelity NuVista to drive my Spendor S 100s. The passive system [ Audio Synthesis Passion Ultimate, Meridian 605s] sounded a little underwhelming, just as Dave experienced. Now the MF sounds a little too forward and "in your face" while the passive sounds laid back but VERY revealing, much easier to listen to. BUT, I suspect many would still like the MF better, as I well may the next time I change associated equipment. A good system is like a kaleidoscope, every change you make gives a new pattern.

More gains, better loading. But if you think a preamp is not your thing then a audio buffer also does the job with a little less gain. Some said using an audio buffer instead of a preamp actually sounds better. more transparent etc.

I received my preamp today and I can answer my own question. The preamp improves the sound of my headphone amp. It dramatically improves the sound of both my tuner or CDP. I had two headphone amps going attached directly to tuner and cd player and I've been listening for a week waiting the return of my preamp. On it's return today I notice both the tuner and the CDP do sound a lot better through the pre even just going through the tape out. The improvement is large with the pre adding character to the music making it sound good basically. I can't explain it but the headophone amps alone were not that good sounding until the preamp was put in between both tuner and cdp. Now both sources sound like they should. The difference is not subtle.