Hi,
I got a Puritan PSM156 a few months ago, and it has made a significant difference in cleaning up harshness in the upper midrange and improving openness and bass detail. I added a dedicated ground rod using their GroundMaster. That improved things further. I swapped out amplifiers, and the improvements persisted even though the amps retained their distinct character. The PSM156 replaced and AudioQuest Niagara 3000.
I expect the biggest source of noise on the line is all of the switching power supplies on the same circuit (TV, NAS, DVR, etc.). About 20 different devices.
Definitely check that your outlets are grounded and have the correct polarity before getting a power conditioner. It's amazing how many outlets are incorrectly wired.
The Puritan website has information and links to reviews.
http://www.puritanaudiolabs.com/products/master-purifiers/psm156/
