Is there a MIDI write feature that will let me export files to Garageband or other sequencers?
Not in the beta version. We hope to add that feature in the next release, as we realize this is a priority for many users. Meantime, a workaround is to record the Sequer using audio capture software, then input this into a Sequencer and add other layers to it. There is also MP3 – MIDI software that you can try.