I had all the same issues described by many trying to install the beta and now the official version (not sure if they're different) using usb, midi, bootloader etc. I had many different issues while trying different configurations, the most common being an incomplete countdown, stopping around 224. I never reached the second countdown until it finally worked today.
Just thought I would post as someone who was very convinced it wasn't going to work for me, and spent many many hours trying, to say that it did eventually work. So depending on how much frustration you can take it may be worth persisting.
For what its worth, what finally worked for me was:
Sysex librarian on OSX 10.10.5
Default Buffer, and speed at 80%
emagic MT4 MIDI interface
Bootloader mode
I tried so many times with so many different combinations of things, I feel like it was just luck when it eventually worked, but it did...