It's the massive teflon capacitors that need the break-in time. I have a ARC Ref 10 preamp and I know it can be an agonizing process to wait for the full blume and potential, but as others have said its well worth the wait. I can honestly say, having listened to and owned many other preamps, the ARC Ref 10 is the best I've heard (after 600 - 650 hrs of break-in). It's within a hair of the VAC Statement that costs over twice as much as the Ref 10. Hang in there your patinece will be rewarded.
Ray
Ray