Queston On Burning In A New Preamp

Ideally you want to feed the preamplifier a signal. In theory, the more diverse in spectrum the better. Since you've been using you CD player an excellent signal generator is the XLO/Reference Recordings Test & Burn-In CD. Specifically track 9: System Burn-in. Best of luck. (In a pinch FM white noise is also reasonably effective.)

Power supply will take the longest to settle, probably around 200hrs. Signal path - usually 100hrs it will be good to go. in other words keep the preamp powered on after you ran signal thru it for 100hrs. Doesn’t hurt to listen either. It’s not a quarantine. Lol

Let us know if you hear any change.  I went through this a year ago with a new Marantz PM10 and there was no change.  Mind you it is always a good idea to give everything a chance to settle in and take form.

I'll keep you posted after 100 hours

It doesn't even matter that you're "burning in" your component because there's no objective evidence that it makes a difference in the sound.