Adding external audio to existing car sterio. Toyota Avensis B9010

[Sprutbærsj]

Hello.


TL;DR: Want to connect phone to the car. Schematic from automotive shop. Can't understand shit. Need help.



Background:
I was hoping there was an easy way to connect external audio (aux, phone, usb...) to my car. This is the unit without the option for Bluetooth and have no existing line-in connection that I have found.
My local shop could support me with what they have in terms of schematics of the car (see below).
I can't find anyone online that have worked around or found an easy solution to this problem. I was hoping not to change the enitre unit as it costs 7000,- nok (~$850 US) for a retail one (from dealer). Ebay ones go for 4000,- nok (~490$ US). The cheapos online goes for anything from 2000,- to 4000,- nok (240$ - 500$ US). And then there is the problem with connections and what not.
I have found some third-party devices that could(!) support the unit, but some specify the B9010 as not compatible.
It is possible to remove/reuse/reconstruct/destroy a compartment above the existing unit and place a separate device there. It is a useless compartment anyway.


Situation:
Add external audio to existing car stereo, video is bonus. Less modification to existing setup is ideal.
Additional screens are possible and might be preferred in terms of backing-sensors/camera and what not.
External FM transmitter is possible, but strongly preferred to avoid.


Preferred parameters:

• Automatic power on/off
• Handsfree
• Aux
• Onboard storage; usb, sd, hdd
• Spotify on unit
• Connected to buttons on steering wheel
• Rearview camera / parking sensors

Solutions:

• Substitute entire unit
• Third-party unit
• Third-party device
• Construct new unit; mini-pc..?
• Seperate/additional amplifier to speakers
• FM transmitter to existing unit

Material:

                       Budget: ~400$ US

Original unit from ebay: http://tinyurl.com/nh2vnu3  ,  http://tinyurl.com/nmhtfup

Third-party device (might not be compatible!): http://tinyurl.com/oxd75fy  ,  http://tinyurl.com/nz29z6l



Link to schematic 1/2: http://tinyurl.com/pxqsds9
Link to schematic 2/2: http://tinyurl.com/qgpnhh5


All help, feedback, tips is much appreciated

[Sprutbærsj]

Interior: http://tinyurl.com/o6dnu5s  ,  http://tinyurl.com/purhocq

Backside of B9010: http://tinyurl.com/naefnpj

Unit removed: http://tinyurl.com/nej2omp


Good thing I know how to edit