I agree with the idea of going first to check your AC power.Change the outlets first. then check your phase orientation on your AC cables. Then upgrade the power cables.If this does not solve the problem, then go for other interconnects, speaker cables, etc.
smoothing those sibilants...
I appreciate the feedback on the interconnect post I made a few days ago, and here is my next question: If I am attempting to smooth out the sound of a "low-end-of-the-high-end" system, reducing grain while retaining detail (and looking for a warmer more "classic tube sound"), where is my energy/$$$ best spent? Would it be the digital source itself, the interconnects, the input tubes, the speaker cables, or the speakers? Or something else? (System info can be seen under the post entitled "need interconnect advice", and there are some new interconnects on the way.)