Sorry guys, I was out of town for the past few days, but Im glad if I could help.
I was searching on ebay a plug and play bluetooth receiver but I was not realy looking forward for the 30days shipping time, so I went to the local chinese shop and bought one of these, they seem to be quite popular.
https://goo.gl/j1kHBH
I payed 3.5$
First I will tell you my experiance with the device, and if you like what you see I can explain how i did the conversion.
I used the unit for 2 months.
The audio quality is overall good, I tried comparing it when playing directly to the aux cable and the audio sounds the same.
It has one problem, but it seems common on that type of devices. There is a high frequency sound comming from the unit when is connected to the charger and there is no audio input (from the connected device). The sound itself is dependable on the engine rpm, so its a ground loop issue, it sounds like a turbo
Just to note, the sound is not present when playing, and can be removed by a ground loop isolator (or maybe a big capacitor ?)
The Mic quality is not very good, sounds like you are speaking from a bucket, but is good enough for calls and google voice recognition. But what to expect from a cheap unit.
By the time I worked on the conversion, I could not get good info on the mic type, but on the board of the unit there is room for a external microphone, so that is the next upgrade.
The unit itself plays "power on/off connected and pairing" sounds in english and they sound good, there is a two led indicator, and you are interfacing with the unit via a button.
After the two monts, I took apart the unit, the battery inside was like a baloon, so I removed it.
The good thing about the integrated battery is that the unit does not power off when you turning on/off the car and it stays connected to the device.
I replaced the battery with a LM317T regulator adjusted to 4V and because I was
Connected to the cigarete lighter wiring, the unit was powered on only after turning the key. In future I will partialy rewire the cigarete lighter to take power from the gloveboxlight ( its stays on for 20min when car off) so the unit stays on when main power is off, or you have a engine stall or similar.
All this can be avoided if bluetooth module would be installed into the built-in radio, which is not so complicated, but takes more skill and some wiring diagrams