I may be a bit late to chime in on this but never the less...
I have the DV P75 mk2 running with my Well Tempered Amadeus. Both use very similar switch mode PSU's and both introduced ground loop noise into my system. I replaced them both with locally made linear regulated wall wart PSU's. No issues now and all is well. The technician I spoke to mentioned that he had plenty of experience with cheap switch mode PSU's introducing ground loop type issues into all sorts of situations. He also said Switch Mode PSU's are just cheap and that's about it!
Very helpful he was
Also I feel the battery way is worth a crack. Where I live some times the power supply just seems really bad. Certain times in the weekends are worse. Almost as if the whole street has all the appliances going at once. You know, everyone has the washing machines and vacuums going at the same time. One time when this was happening I connected an old style isolating transformer to my main mains plug and presto. It all sounded better, smoother, less sort of noisy and frenetic.
Just an observation.
Craig.