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.
FM 304 Groovebox - video export
FM 304 is a fun and affordable app but one of its limitation is that it cannot record and export its audio and it's not Audiobus compatible either.
One workaround is to do a screen recording and then either extract the audio from the video or add audio tracks to it in a video editor.
I did the latter in this video, adding a second audio track of vocal samples from my Memory Collection packs. I exported the video to my PC to edit it but I could have done it with Lumafusion in the iPad too.