I have my audio system connected to my router via a 50 foot CAT6 ethernet cable. I use Powerline adapters for my TV setup which involves an outdoor antenna and a Tablo over-the-air DVR (works fantastic, BTW, as long as you have a really good antenna signal feeding it).
It very well may be a placebo effect, but my audio system sounds harsher (even with vinyl) until I unplug the Powerline adapters. I do have an Audioquest Niagara power conditioner....
I also like to turn off my hot tub and fridge at the breaker box and make sure all dimmers are off before doing any serious listening.
I have thought about doing an experiment by running a temporary long coax cable inside my house and put my modem and router closer to my audio system, the theory being that it might be better to have a long coax run and a short ethernet run. A similar theory to having my monoblocks right behind my speakers? I'm using .5 meter speaker cables and roughly 4 meter interconnects from preamp to power amp