Much to my chagrin, the difference was minimal at best.
This matches my experience. I find differences are relatively subtle - often far less than typically found between a good recording and a bad one. I had a friend over and he could not hear the benefit of a separate DAC versus the straight sound from my DSP preamp. I have to admit it was close but once you pick up on the slight differences and begin to know what to listen for then it becomes much more noticeable. However, I'd agree with anyone who said it was not "night and day".