I have installed the DSP Audxeon D1680 a months plus and I learned and did the tuning myself.
On my Flagship, just by adding DSP only, it is definite much better that it can help to boost the bass and mid bass; or getting crisp on mid to high freq range.

The original speakers are not bad, only lack of bass and some mid bass range, will DSP can set to have more bass or crisp in the front or rear speak.
I'm still learning to tune, increase bass may come a bit of sacrifices on high frequency range or vice versa if your want more crisp sound at high freq. However with the DSP, you can also tune front speakers more crisp and rear more bass and mid bass.

However, a week ago I got myself an active subwoofer too and I would say it is amazing sound now. It make my tuning much more easier and flexible.
-Front speakers focus of mid and high freq, filtered low freq.
-Rear speakers filtered a little on the low freq and may it covered from mid bass freq range upto high freq and boost on high freq range.
-Active subwoofer, didn't do any change, flat signal direct from DSP to active sub. Only adjust gain and added little bass boost from active sub. itself.

Measuring with pink noise, I can now easily tune to audiophile profile (flat across the freq. range and slight higher of high freq range) with the original speaker + active subwoofer comparing to without active subwoofer.

Again I'm a noob on this and still learning here, however if you are using the same DSP, I'm gladly to share my setting profile with you.

Here is my settings, hope someone can provide the feedback if he/she tested on his DSP.

Attached zip containing "20210512-MoreBass_CH6.S6Set" for Windows for Audxeon D1680 and "21May10c6Bass1.20" for CAR_DSP app on phone, this must be put inside \Root\CAR_DSP folder.
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Your question for blue wire, it is the ACC/remote signal, on default you can leave as is it without connection.
For me, I use this ACC for the active subwoofer.
Refer to mryellow19 at below.
You're absolutely right, the audio signal and remote/ACC power coming from DSP.

From battery
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Go into grommet
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Coming out near the socket below BCM/ECU box.
View from bottom up.
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Another view of the BCM/ECU from glovebox before pulling the cable.
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You will need to dismantle the glovebox and the cover behind & underneath the glovebox to get access.

For glovebox
- 2 plastic screw(that work as a hinge) inside the box. You can use 20sen coin to remove it by turning 90 degree (rotation direction depends on left or right side).
- I think only for FS/premium model got a damper on the right side of the glovebox that you need to remove. It is just snap in on to a clip, you need to press to release it.
-After removed above, you can pull the glovesbox on facing up direction, but I find it easier to pull out if you loosen or remove bottom cover first.

Bottom cover
- Just a single clip at center, once removed, you can the bottom on down direction, there are 2 snap hinge latching vertically at left and right. Then another 2 latching horizontally at the back.
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Back cover behind glovebox.
- 3 screws facing you that can be open using Philip screwdriver or socket.
- Then another 3 screws on top side, can only open with Philip screwdriver.
After removed the screws, you can put your fingers inside the cutout hole on top to pull the cover out facing you. The cover is also hinging on the bottom cover if you didn't remove it earlier, thus it is easier to remove it first.

From here, you can also push the side cover near door at the dashboard to allow cable to pull to passager seat.
For the underneath center console/dashboard it is also easily open by pulling (no tool required) . It is secured by a single clip that can act as a hinge. So you can just pull the small panel opposite to the clip. This is to allow you pull cable crossing from passager to driver side.

Can someone assist to advise what the below highlighted means? I've tried turning it on via the infotainment system. Does it mean that my car will horn and flash lights when I lock my car? Because I still only get lights feedback when I lock my car. Thanks!