How to break in a tube preamp?

Breaking in your preamp does not require that your power amp be on. Just do what you said--connect your digital gear to the preamp, put it on infinite repeat, turn your preamp on and use your regular volume setting. The preamp has a loading resistor on its output (to prevent any DC from building up if there isn't an amp connected), so running the CD player and preamp in this fashion is fully equivalent to listening to music through the entire system.

I recently purchased a Modwright Ls100 which has the same break-in period as your amp and was told by Dan Wright that I needed to play music for the caps etc to properly break-in, versus just leaving the amp on. Unlike Ahendler's experience I have noticed a significant difference in this amp as it continues to get "mileage"

Thank you everyone for your input. Much appreciated.
I am looking forward to hearing the post burn in period. By all accounts the teflon caps are wonderful once they have considerable time on the clock.

OH thats a tough one!!

I own a linestage with teflon caps, but i would never say that they are universally good--it is all a matter of voicing. A cap that works well in one design, and to one person's taste can be really bad sounding in another application. I've heard gear "upgraded' with Blackgates and teflon caps that sounded really bad. I know of people that search for fifty year old caps that sound great in certain designs (another linestage I own uses these kinds of caps).

There really isn't such a thing as good caps and bad caps, it is more the case of finding the right cap.