Done it!

I knew the scripts worked, I had tested it with various other dbus signals (such as keyboard open / closed, screen locked / unlocked). I also knew that the helmet would connect and I could start music playing myself.

Something I should have explained first - it's a bluetooth motorbike helmet, so it makes my life much easier if I don't have to touch the phone (voice command would be very nice though!).

Anyway, the only reason I could think of as to why it wasn't working would have been if the dbus wasn't being told to look at the correct thing. Using this command:
I could monitor the signals. I connected the helmet and it threw up about 6 (I didn't actually count) different things going on. So I typed one of these into the dbus file. And it worked wonderfully. I repeated the same process to see what I needed to tell it to look for on disconnect as well.

So, there we go. It wasn't so bad after all.

Only thing I have to look at now is why, upon restarting the phone can't I use any command to start music playing - I have to press the play button on the widget instead. Anyway, I am happy with the results!