Thanks Tony,
I think that you have politely proved my suspision that I am far too impatient :)
I was also thinking of making some test files in Goldwave but thought there may be a good set that is commonly available.
I never noticed the mastering differences with my old Kenwood 10xCD changer on random but I suspect that was because I wasn't listening as intently as I have with the empeg. I think I may be trying to listen for artifacts/problems with compression and therefore paying more attention to detail than I used to.
I will take your advice and make EQ changes sloooowly over a range of CDs.
MK2 Red S/n 949
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MK2 smoked 32Gb S/n 090000949
MK2a Blue 20GB racked and out of sync