I've done the inside of the cover, and as much of the chassis as I could get to easily. If I were to do it again, I would remove the transport and circuit boards and do the entire chassis. Make sure to damp the "loose" corners of the cover (at the back). I also put Dynamat on both sides of the pieces of angled chassis material that support the transport.
I used rope caulk to eliminate vibrations in the front panel and around the transport feet that are not screwed down. If you have the upsampler, you can secure this board by placing rope caulk between the upsampler board and the side of the chassis.
I placed a small spot of rope caulk between each of the capacitors on the main board (the big cluster of capacitors). They can vibrate against each other.
Tighten ALL of the screws inside the unit, including the one that mount the circuit board to the front panel.
If you tap on the various components, you'll find the loose items and rattles, such as the little clear plastic covers near the power supply.
Another helpful tweak was to place two small bags of sand on top of the cover - one over the transport area, and one over the power supply. I used 1-gallon zip-lock bags with just enough sand in them to make them about the thickness of a magazine when folded in half (with the sand spread out flat). If you place your ear on top of the unit when it is on (but not playing), you can hear the vibrations. The two sand bags eliminate much of this noise.
The biggest problem with the Ah! is the cheap plastic transport. It is rather loose and very difficult to damp competely.
I hope this helps. It's worth the effort.