Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
Free desktop music visualizer
Just discovered the projectM opensource visualizer which grew out of Milkdrop on WinAmp. Pretty amazing visuals - an inbuilt library of presets can be extended with any that are Milkdrop compatible - there are tens of thousands out there...
Basically, you can have the app listen and react to any audio (you'll need something like Soundflower or Loopback on a Mac) and there are hotkeys to interact live with the visuals...
Github page here: https://github.com/projectM-visualizer/projectm
Free Steam download here: https://store.steampowered.com/app/1358800/projectM_Music_Visualizer/
I couldn't find any up to date installer packages on github, just the source code so looks like Steam may be the easiest way to grab it for Mac / Windows at the moment - I'll check with the dev team.