phono preamp break-in machine

Drubin, the disc being played doesn't change the output voltage of the CD player, so the warning remains valid. Reversed RIAA equalization on the Granite Audio disc allows the CD to be listened to after being put through a phono stage. You can actually use any disc for this break in, but you would have to turn your preamp volume to zero for a normal CD.
Having said all that... just play records. If you bought a nice phono stage (I'm assuming you didn't DOWNgrade), it should sound very good to you on the first day, and will improve more with break in.

Cheers.

I had my phono stage modded by Bill Thalmann. He used Teflon caps and hook-up wire with Teflon dielectric. Since it was recommended I put 400 hours on the caps, I bought a KAB PreCon LP, inserted it between my DAC and my phono stage and forgot about it. (www.kabusa.com) With a small business and three children, 400 hours seemed forever.

I do have to say that the sound of the modded phono stage after 400 hours of burn-in was vastly improved over the unit upon arrival.

Tfkaudio: The disc being played doesn't change the output voltage of the CD player

Of course it does. The output voltage changes continuously in proportion to the instantaneous amplitude of the music, or in this case the test tones. If the tones are very low in level, the output voltage will be also.

That said, I strongly second Elizabeth's comments.

Regards,
-- Al

Why risk anything? Can't a preamp burn itself in properly by itself over time, or do these "burn in devices" condition the preamp in a certain way? Personally, I have to believe that any reputable designer would have tested the prototypes after they were broken in and then made adjustments so that the production models ran properly.
If I were going to invest in anything, I would invest in a variac transformer. I'd use it to gradually condition the equipment to full voltage. Things would probably last longer too.