I'm posting this so anyone who owns a Roland A-Pro midi controller and is frustrated with the unusable aftertouch can improve it to some degree. As stock, it requires a ridiculous amount of force to activate. After this fairly simple mod, it is bodering on usable. I don't take credit for this mod - it came from another forum - I'm just adding some photos to make it clearer. No responsibility taken for destroyed boards - only do this if you are handy with a screwdriver and know about delicate electronics!
Firstly, remove all the screws from the underside of the board - except for those directly under the keybed. On the A800 there are around 12 larger screws and then 5 smaller ones under the front lip of the board. Be careful not to let the top panel fall or move too far from the bottom assembly as it is joined by several flat cables. The mod can be made without disconnecting these. Slide the top panel forward to clear the lip of the keys, then lift slightly. You will see a small yellow trimmer potentiometer(indicated by arrow in photo). Carefully adjust this fully clockwise with a small screwdriver. Refit the lid and screws and the aftertouch should now be considerably easier to activate. I measured that it took about 750g of force.
Even after the mod however, it's still not great. I think that the key landing felt is too thin and hard to compress. The aftertouch also relies on some key flex to work - it's much harder to activate from the key tip than it is from 1/3 of the way in. I think there is potential to replace this stip with a softer felt or rubber to allow better aftertouch control. Better still, Roland could have built it right in the first place. Aside from the aftertouch issue, I think the board has a good feel and is nice and light.