Conditioning/Burn-In Method

Ah, well I could do that but I'm burning in the speaker cables, too, though they have a hundred or so hours head start - got 'em before I bought the ICs.

Elizabeth is correct that in the great majority of systems the DAC-to-preamp connection conducts a larger signal (i.e., a greater voltage) than the preamp-to-power amp connection. On the other hand, though, what is relevant to your question is the amount of current each cable is conducting, which in addition to depending on the signal voltage also depends on the input impedance of the component the signal is being provided to.

So for example if the input impedance of your power amp is considerably less than the input impedance of your preamp, it may be that the current being conducted by the two cables won’t be all that much different. But on the other hand if the input impedance of the power amp is higher than the input impedance of the preamp, and perhaps even if the two impedances are approximately equal, interchanging the cables between the two locations when you believe the DAC-to-preamp cable is reasonably broken in could very well be worthwhile.

Regards,
-- Al

So, paraphrased: Swapping cables won't hurt, but might help.  Check.

And, as others have said, get something like Ayre's Irrational but  Efficacious! CD burn in disc, along with swapping out the ICs. 

All the best,
Nonoise