Notus, I am using the 840 and 940 pads but with one modification. I removed (cut out) the foam backing on the shure pads, and used the stock foam ring that came with the AKG. The shure pads in their stock form are very dark sounding and I wasn't excited about it.
This combination is by far the best I've tried. Much better than the shure pads unmodified.
The sound is extremely neutral, and no range seems to be emphasized. This results in really good imaging and instrument separation. Textures and resolution is also improved over stock AKG pads. Bass has a nice, punchy feel. Midrange is right about where it should be and is smooth sounding. Treble extends nicely and is slightly forward but didn't seem fatiguing.