Re : Declaring an array of recordings using minim

Recordable is an interface.
From JavaDoc:

All Known Implementing Classes:

AudioInput, AudioOutput, AudioPlayer, AudioSample, AudioSource, SignalSplitter

So you can put an instance of any of these classes there.
Apparently, you can get one with:
minim.getLineIn()

1.     recording[x] = minim.createRecorder(minim.getLineIn(),
2.                   "recording" + x + ".wav", true);

Untested, just making deductions from the JavaDoc...