Chain of command:
The source: Not much you can do there. GIGO or "it is what it is". Find your best source.
The DAC: You're not asking about that.
Cables: Well, there's the digital from the DAC and the ic's from the DAC to the pre. Maybe you could squeeze out a little more enjoyment there.
The END: Room, speakers, amp/pre. I had "enhanced success" yesterday when I changed "just" a digital cable. I have a couple systems. I enjoyed my Maggie/ss a little more, then last night I fired up my SET system and it sounded a little better also.
Done squeezing for awhile.