Failed resistor mod update.
I took some time last night to see why my MA900 headphones failed. The schematics and pictures posted here were correct on my pair.
The failure issue was that the leads from the board to the voice coil go ABOVE the board NOT THROUGH the board.
So use extreme caution if considering removing the yellow blob of adhesive on the board; that adhesive likely covers the (very delicate) leads.
I think the leads go to the outer edge of the board at what appears to be a small "red dot" at the outer circumference of the frame. The wires are are then snaked down towards the voice coil.
A few people here recommended soldering @ resistor pads; I think that is wise advice and a much safer alternative than going straight for the leads.
Disassembly confirmed the headphone's overall industrial design is quite good; engineered for efficient production and performance. A lot of foam that will unfortunately deteriorate over time. Definitely not user serviceable.
I will try mod on second pair, which I quite enjoy.
Also noted that the leads were glued with a clear adhesive directly to the driver (from outer edge to the coil). That was a surprise.