I usually use a fpII as a pre. It has been modified to lose lots of signal and I never got that to work quite right, but works great on the crack. I have Beyer dt990s (600ohm) and dt880s (250ohm). On a speedballed crack there is plenty of volume at 10:00 then earsplitting starts at about 01:00.
I do have a non-speedballed crack that I didn't think to try until your last question. Using the non-speedballed crack I would say comfortable level is at about 11:30 and getting loud at about 12:00. (I do consider my ears to be sensitive; others may not
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My understanding is that the dt990 and dt880 have the same drivers, so our phones should perform about the same. But there are many more variables; mains line voltage, specific tube outputs (a tube output may vary slightly from others), actual source levels, different peoples ears, and even variability in recording levels between listening materials. There are others here that know much more than I, but I suspect the difference between our two setups are within the normal range of variability.