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.
Why do preamps improve sound of CDP?
I have tried listening to my CDP through my preamp and bypassing my preamp going from CDP directly to headphone amp. If I go through the tape out of my preamp the sound is even nicer than direct from CDP to headphone amp. Why is this?