Per app audio device output selection
Soundflower used to be the thing for that kind of task, but it's fallen by the wayside a bit over the past few years.
It was originally by Cycling 74, but then Rogue Amoeba took over the hosting. They never did anything further with it &amp; eventually it was open sourced &amp; a couple of newer versions were produced.
The latest I'm aware of is a signed v2.0 beta at https://github.com/mattingalls/Soundflower/releases though I've not tried it myself since the older 1.6.x versions started to fail on Mavericks.

Your fully-flexible &amp; El Capitan-compliant alternative is, as you discovered, Audio Hijack - which is extremely good at what it does, but is pricey for a one-trick pony.

See https://apple.stackexchange.com/a/203009/85275 for some configuration examples.