When I was working on this side of things for the FMDrive Vsti, I have made of bunch of testing on the hardware.
Here is a possible approach of  the YM2612 chip "Ladder effect" on the DAC side.
Further informations could be accessed on the web.

when setting the output of a channel to "mute"
Playing some notes here do not play silence but the same line as normal except (center) already distorted from the start and at a lower volume.
The very last ms ends with quantized effect on top of that.
TL as almost no effect on the slot until near max attenuation.

I think that the distorted line and the clean line simply adds together from the start.
The fact that we only ear the last portion is obviously because, as the clean line reaches low volume, the frequency richer distorted part underneath become prominent and that is also why some sounds seems to have a longer tail on the hardware then on clean emulation.
The positive portion of the sine also seems to be slightly shifted to the right the more the attenuation goes.
So there might be something in here just before MOL and MOR...
Here is a wave recording of the effect.
1// B4 D7 and D6 are set (center)
2// (mute)


This is basically how I have emulated the process in a clean simple explanation.

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