Exactly,
The bass problem you are seeing is common. Damping the rear of the driver directly, filling the cup with cotton, or sealing vents will help hugely. This limits how much air can move, keeping the driver more in control.
For treble, try sound dampening foam on the back of the cup, this helps with reflections.
I use 840 pads on my mk2s, and that reason alone has scared me off the mk3s. Pad choice is severely limited if you want to keep the baffle vent system with the mk3s. If you seal those, you basically just turned them into mk2s heh