As Sugarbrie states, dedicated AC lines provide excellent benefits regardless of what else you do.
As for your original question, I'd recommend investigating the Foundation Research LC-1 and LC-2 dedicated and passive in-line power conditioners. Marty DeWulf of Bound for Sound reviewed these last August and claims these to be the best in the business and purchased them for his 'big rig'.
I've been using these for over two years and the benefits are tremendous, including the elimination of any negative sibilance.
BTW, they come with their own built-in power cable and cost about as much as a good power cable.
-IMO