When you use a software method to shutdown Rune Audio, the Pi is also in shutdown. It is not completely disconnected from power, so it still uses a tiny amount, but all USB devices are off. My Wifi dongle, wireless keyboard dongle, flash drive, HDD, and my HIFiBerry DAC+.
I measured about 7-8 mA current being used in this state. (Much less than my PC with WOL activated, or my video receiver.)
So, if you are using a battery power bank, in 24 hrs you would consume less than 200 mAH. A power bank with 10000 mAH capacity would last over a month (theoretically).
The problem is not a soft OFF, but a soft ON. For that, you need some additional hardware, software alone will not do it.
From a thread in the official Raspberry Forum:
Your RPi is perfectly capable of generating WoL packets for any destination machine on the same LAN segment. The thing it can't do is react to an incoming WoL packet.