Upgrade of MMI Basic Sound System Audi A6 4F up to KW35/2008 (Articles)

To upgrade the Audi A6 4F MMI Basic Soundsystem (up to chassis code 35/2008) with only speakers in the front doors to a decent sound system, it usually requires a significant amount of work.

The following article describes the necessary steps to integrate a 4-channel amplifier into an existing sound system, as well as the retrofitting of speakers in the rear doors. Time required: approximately 1 day.

The advantage of using the existing components (radio/CD/changer) is a relatively straightforward extension (otherwise, various control units would have to be replaced and additional cable harnesses would have to be installed), as well as maintaining the integration of the system (when replacing the radio/CD/changer with third-party components).

This involves tapping the signals for the speakers at the J523 control unit and feeding them to the high-power inputs of the amplifier. Also, the mass for the inputs and the remote signal to activate the amplifier.
When connecting the high-power inputs, please note that only ONE speaker connection should be used per input, and the internal coupling capacitors of the amplifier's input stage must be correctly polarized!
When using the Nano-404, we use L- and R-. The power supply for the Nano-404 is, for simplicity's sake, provided via the fuse for the cigarette lighter (30A) and the ground point next to the right fuse box.

Necessary Parts:
- Original Bose LS rear speakers, 2x woofers: Part number 4F0-035-415 B and 2x tweeters: 4F0-035-399 A,
- Small parts: 6x Plastic retaining nuts N-911-214-01, 6x Screws N-906-986-06, 2x Connectors 8E0-972-623,
- Speaker covers for rear doors, part numbers 4F0-035-436 A and 4F0-035-435 A (Please note the color code!)
- Speaker cable 2.5mm ² , high-flex, approx. 10m,
- 4-channel amplifier with high-power inputs, the Carpower Nano-404 was used.
- Fabric tape and cable ties,
- Soldering iron and solder,
- Mounting plate for securing the amplifier, 2 M6 nuts and various small items such as screws, cable ties.
- Combination wrench, long Phillips head screwdriver, 8mm socket.

Installing speakers in the rear doors:
- Installation of door trim, unfortunately, force must be applied here, as the visible mounting brackets on the image make it very difficult to remove the plastic clips (not visible as they are not inserted) from the door. No need to worry about using force; broken brackets can be easily repaired. Procedure: Remove the upper speaker cover, for example, by prying it out from the direction of travel with a knife. Unscrew the retaining screw. Remove the retaining screw at the bottom of the handle with a very long screwdriver, remove the retaining screw at the very bottom.
Now, use force from below to pry open the retaining clips of the cover, in order to avoid damaging the cover, for example, use a spatula or similar with a wide surface to lever. Then, fold down the camouflage, loosen the hand-held fasteners on the left and right sides of the windshield frame, and disconnect the wiring connector.
- Extension cable connection to the door: Manual, simply clip out.
- Extending Coverage to B-pillar: At the B-pillar, remove the upper cover by pulling on the left and right sides of the cover, which then releases from the mounting. The lower part of the cover can also be easily removed by simply pulling it upwards.
This clears the way to the door openings.
- Door trim repair: old soldering iron, utility knife, 6.5mm drill.
- Installation of speaker covers.
- Assembly and wiring of LS. Prevent rattling/vibration through secure fixing using acrylic sealant, textile adhesive tape, and cable ties.
- Assembly: Attach/screw the speakers onto the original clips, the tweeters can simply be clipped into the existing brackets. Pay close attention to the correct connection of the speakers.

Installing a 4-channel amplifier under the glove compartment:
- Removal of glove compartment,
- Manufacturing Bracket (Holding Plate)
- Pay attention to the wiring and ensure the correct connection of the speakers.
- Assembly.

Wiring from B-pillar - Glovebox
The audio cables to the rear doors are routed under the sills to the left and right rear, and these do not need to be removed. Removing the left-hand footrest is helpful for routing the cables under the carpet in the footwell. All cables are securely fixed and planned to be routed in a way that avoids future short circuits caused by friction or sharp edges.

Subwoofer to utilize the remaining 2 channels as a bass booster
The remaining two channels of the amplifier could still be used for a subwoofer, for example, Mount under the glove compartment or in the trunk.