I've just realised its entirely possible to DIY this. Rather than have the MHL HDMI cable from the phone connected to the Mimics X2 device, you could just connect the Netgear PTV3000 to it.

I think I'm going to attempt to get all these bits together and make them work. The VW RNS510 unit I have in my car at the moment could go on eBay and fund most of it!