Unfortunately, I am many miles from Tallahassee. I am currently near Seattle. Just had an earthquake at 2:50 this morning! Stereo still silent. Earthquake didn't fix it.
EDITED... Please accept my apologies!
I read your other thread (July 3) for your 2008 GL450... Congratulations!
It seems that you have NTG2.0, which is the same one I've had on my previous 2006 SL500.
Generally speaking, MB amps are die hards and has internal electronic protection systems that can effectively prevents overloading; so nevermind wht stereo shops claim. If you check the used MB stereos on Ebay, more than half of them are sold by shops for known reaons.
Based on my 2010 GL550 (X164), and from the symptoms you listed I can tell that the plugs at the back of your head unit (on dash) has some loose connections of some sort. Please take the unit out and snap pictures of each an every plug to confirm that (1) they are on the correct locations (2) perfectly plugged (3) to confirm that the male fibre optic bus connector of 2-orange hard FOs are perfectly connected on their female plug on the head unit.
The main big connector has multiple plugs mounted on it, and any misplacement of these will result in no audio (and in my case, no one can hear me speaking on the phone bluetooth connections...misplaced the plug
Now. you may ask, why the heck anyone goes there to plug/unplug things?
The answer is: It is possible due to the installation of VIM Modules (Video in Motion) which enables DVD playing and GPS change while driving. This module hooks up between the OEM harness and the head unit and it will involve fibre optic displacement.
There are UTube videos to teach you how to take the NTG unit out of the dash... It is extremely easy.
Bring back the requested conformations and we can discuss further