78 watts or even 100 watts if the AVR idle figures are understated, is still less than 1 amp, hardly worth worrying about. The other equipment may be another matter, and I would be concerned about any non-audio devices on the same circuit. Nevertheless, in real world use, a multichannel system does not draw that much power at normal listening levels.
My HT system is on a single 20A circuit Components on that circuit include 100W x5 AVR, 210W x 2 amp, 150W 12" sub, LCD TV, DVD player, 2 cable boxes, all plugged into a Belkin PF-60 line conditioner. That system draws 2 amps at idle. While watching movies at normal listening levels, it draws between 3-4 amps. Comparison of the current readout of the Belkin unit against that of my RMS reading Fluke clap-on meter confirmed the readout to be accurate. Similarly, my 2-channel system, with 600W x 2 amp @ 4 ohms, draws around 3 amps at normal listening levels.
As a newlywed many years ago, I started out in an apartment with only two circuits, 20A in the kitchen, and 15A for the rest of the place. I made do just fine with my system on that one circuit and amps in the 200 to 330 watt range.