20A circuits generally use 12 ga romex. I would check the outlets you are planning to use. Many 20A outlets will not accept 10 ga or larger wire, so you could be locked into 12 ga. Perhaps audiophile type outlets are more flexible on wire sizing given their target audience, but the time to check on that is
before the romex is in the wall.
Just a thought, Are you allowed to run Romex in your house? At one point the NYC building codes mandated that all residential wiring be done using BX cable. Not sure what the rules are today, but it is something that you might want to check out before you get started.
Also along those lines, I seem to remember reading or hearing somewhere that BX cable was preferable of Romex on a sound quality basis. I believe Jim Marks had his dedicated outlets wired with BX even though it is not required in Nassau County.