Peak means peak. Any EE would know what peak means. RMS only applies to sinusoidal waveforms. RMS Voltage is computed by Vpeak
times square root of 2, RMS current is calculated by Amps(I peak) times the square root of 2. The rest is simple Ohm's law. Check your EE textbooks.
No one can use program material to spec a power amp. Sinusoidal waveforms are always used therefor any reference to program
material is completely irrelevant in this discussion.
Peak power may very well be applicable since transformers are rated with Volt Amps. Also, my calculation seemed to match what Outlaw
indicated in their post. As a telecom engineer I've never speced parts for a commercial audio amp and don't know what standard practices are used in the process.
As a DIY audio designer I've always went for overkill since I'm not designing to a price point. In my 450 Watt sub amp I used peak power and a 80% derating, the transformer is a 550 VA unit. This is a bit small but I've never had a problem (you can't be that picky with surplus parts). What do you use in your designs Charlie, I'd really like to know.

I did notice that Pass Labs 125W 5 channel amp has a maximum power spec of 600 W. The Pass amp is much more expensive and
conservative design than an Outlaw amp (or any of the other cheap amps, Rotel, ATI, B&K ect) and appears to be rated in the same manner as far as power dissipation is concerned.