I have the Network Acoustics (NA) Eno2 'Ethernet Filter' system with the NA LAN cables (the cables come with the Eno2 as a package deal option) and it made a significant difference immediately noticeable in soundstage dimensions, image clarity and instrumental separation. The science behind devices like these is readily available on the internet. More importantly, in a higher end system devoted to digital sources like mine, the devices simply work their magic, and apparently for many others as well.
I just don't get why, BEFORE open-minded experience of these devices in one's own system, one would discount their efficacy.