Dedicated ckts? They aren't the 'end all be all' in providing clean power to componenets. All they do is limit, NOT eliminate, in house 'born' artifacts. Remember, voltage and current need a path to flow. A complete round trip path. The neutral side of the power lines, dedicated or non dedicated, are tied together at the ckt breaker box. Consequently, so is the common or ground leg.
Through those two paths, one more so than the other unless there's some default somewhere, ALL the house power is in the end seeing each other's strengths and shortcomings.
Dedicateds do reduce issues, but they won't eliminate them.
The suggestion of true isolation as said above, by isolating BOTH the neutral, common and powerlegs via Tformer, and iso'd ground is the best bet. Period.
Even still, there can be issues, albeit depending upon the build and design of the iso Tformer, remember, even that is attached to the incoming power line to the home.
I believe that incoming feed is primarily where we get much of the nasties we endure, ignore, or deal with in our audio & video systems.... not from the home itself. Or at least not as much.
That's why so many feel it a more cost effective way to go by using dedicated ckts + a PLC. So unless you're starting from scratch and just now building a dedicated entertainment room, just join the pack and do the now priceier "Agone try & buy shuffle" to find what fits the billet for you and your's.
