Update:
I've tried so many different things and I've finally given up on trying to make the Android work properly with the I3.
It kinda works with Bluetooth but the playlists aren't available, you cant search, and you are restricted to the music on the current playlist selected on the phone. Overall, a pretty naff solution. As for Android over the USB, that's just a non-starter. Don't bother trying; it will make you angry and make you go grey very quickly.
So what else did I try?
1. USB Dongle - got millions of the damned things kicking around the house, so I loaded some tracks onto it, plugged it in........and nothing. it could read the device but not see the music. Didn't waste any more time on this one as really, its not the best solution overall due to lack of imported playlists, etc. FAIL
2. Lets dig out that old iPod my wife bought me about 5 years ago... Didn't work at all. I loaded the music onto it but the I3 just sat there 'reading' for 10 mins until I gave up. There's no BT on this ipod so that was a non-starter. FAIL
3. OK, so I wonder if a modern iphone works better than a modern Android? Absolutely it does! I borrowed my sons iphone 6 and it worked really nicely over the USB link and I could search, view the playlists, etc. PASS!
4. So that's great but I converted to Android a few years ago and really don't want to go back to iPhone again. Luckily my son had an old iPhone in the drawer - not got a clue what Gen it is but its OLD! Plug it into the USB and hey presto, it works just as well as the modern iphone 6. PASS
What I've learnt:
1. The BT works ok on all platforms but its not very user-friendly
2. The USB only seems to work properly on the IOS platform
3. If the USB does indeed work on Android platform then its damned well not easy to work out. I'm not a mobile geek but I'm technically pretty clued up and I couldn't work it out.
4. The USB dongle probably works ok but only on a restricted list of audio formats. I don't have time to be converting formats...
My solution is that I'm going to connect my Android via BT for the phone features and keep the old iphone in the car connected to the USB for audio. Seems like the best overall solution for us Android users.
Happy listening everyone