My A2 connected to chassis ground adds body and focus. Adding a D2 to usb creates harshness especially evident on coral works.For chassis „grounding“ I recommend using the M6 grounding bolt situated between the IEC inlet and the fuse holder.
For signal „grounding“ I recommend using a free USB slot. BTW you can use multiple ground leads to multiple slots to increase the „effect“.
*note this is not real electrical grounding, though it can have a significant effect.
Some of you may still be in possession of the ground tweak, the „Setchi“ we used to make once upon a time, the A series of these would connect to the chassis „ground“ and the D series to signal „ground“.
I removed the D2....