RNS510 + aftermarket amplifier

I have a 2012 VW CC (it is the facelifted model but still has a Type 3C chassis) with a "Model D" RNS510 head unit that bears the part number 1T0 035 680 D. It is currently running firmware 5274 without any issues.

Recently, I have upgraded the 8 factory drivers (4 mid-low and 4 high) to a set of aftermarket speakers, which are also working great. Of course, it doesn't take a genius to realize the RNS510 is incapable of driving them to a satisfactory-sounding level and going down this path the next logical thing to do is to add an amplifier and a sub-woofer, since the feet are already wet. The wife will probably disagree but I'll leave that for a separate post.

I went ahead to acquire a 4 channel class D amplifier as well as an 8" sub. Before installation, I saw multiple forum threads (including posts from this forum) that points to some VCDS coding which does the 4 things below if one is retrofitting a factory amplifier:

1. Lower the audio output on the RNS510 from speaker-out to pre-out;
2. Set the sound system to drive active speakers instead of passive speakers;
3. Disable speaker monitoring function;
4. Set equalization to Linear (which is already the current factory setting of my car).

Assuming it also works for non-factory amplifier, I fired up VCDS and proceed to open Controller 37 and make the necessary changes. Code accepted. But to my surprise when I open Long Coding again, the old coding is still there. So I restarted the RNS510 by pressing Alt-Ctrl-Del (I mean < > *). Still the same. I tried coding at Controller 56, same results. Locked the doors and left the car overnight, same. The 10-byte coding is not updated no matter how I try. Frustrating as it is, there was no error message either.

Here is a scan of the controller, which does not change before or after coding:

Code:

---

Address 37: Navigation (J0506)      Labels: 1T0-035-680.clb
  Part No SW: 1T0 035 680 L    HW: 1T0 035 680 D
  Component: RNS-MID      H61 5274 
  Revision: AB001001    Serial number: VWZ6Z7M4006078
  Coding: 04000402040000A0000F
  Shop #: WSC 05314 123 12345
  VCID: 377CA2A0862E84F912-8062

  Subsystem 1 - Part No: 7L6 919 859 J
  Component: SIMA V6  8254

No fault code found.

-------------------------------------------------------------------------------
Address 56: Radio (J0506)      Labels: 1T0-035-680.clb
  Part No SW: 1T0 035 680 L    HW: 1T0 035 680 D
  Component: RNS-MID      H61 5274 
  Revision: AB001001    Serial number: VWZ6Z7M4006078
  Coding: 04000402040000A0000F
  Shop #: WSC 05314 123 12345
  VCID: 377CA2A0862E84F912-8062

  Subsystem 1 - Part No: 7L6 919 859 J
  Component: SIMA V6  8254

No fault code found.

---

So the option left would be to change to an aftermarket HU or to proceed as is. Aftermarket HU also comes with the penalty of losing integration features so I would really want to do that as a last resort. I now have the following concerns hoping you can help:

1. Is the coding issue I describe above common and is there any known workaround?
2. If the speaker monitoring cannot be disabled, once I connect the RNS510 to the aftermarket amp, would the audio output be disabled or it will just log an error code?
3. Which would result in more severe audio quality deterioration, inserting speaker level to line level adapters or feeding speaker-out signals to the amp as-is?

Your help will be greatly appreciated! Thank you :)