Hello. I do still experience the MIDI export not working in Kindle Fire HDX. I also experience the same problem on my Nook HD+ tablet. Both tablets have the ES File Explorer app installed; the ES File Explorer provides some of the export and save destinations for the OS.
Also, if I use email as the mechanism for Send MIDI file, the email gets sent out just fine, but the MIDI file attachment is missing from the received email.
Both the Subject title and the contents of that email are the following text: "/data/data/com.binitex.pianocompanion/cache/pianocompanion_melody.mid - Piano Companion"
I also see a footer message that reads: "The file is generated with Piano Companion: http://pianocompanion.info"