Not having dedicated lines would most likely make a bigger difference than with dedicated lines.
With dedicated lines there are no lights or any other noise generating devices plugged in to that circuit. I still use a P300, with my preamp, transport, DAC, and tuner. Everything in the front end is plugged in to a Dectet and amp in to a PSA Duet.
Over the years I have come to the conclusion that everything matters in a decent audio system. From the obvious, to various tweaks. On their own they may not seem like much of an improvement, but they are cumulative. There are numerous recipes and descriptions on building room treatments. Tips for speaker placement, not everything requires a big expenditure.
And either through a known dealer, or from PSA, Music Direct, or Audio Advisor you can do an in home demo. With PSA, you can get great trade in deals, and no hassle returns.
If my finances changed there would be a P20, and a P15 on order asap.