This one is nowhere near as hard as "I'm having a Key Stroke," but it's a bitch nonetheless.
8-Key Planetary Piano is only more difficult than 4-Key because the visuals are less clear. The inner keys especially are very difficult to distinguish for a newcomer. Unlike the speed-based achievements, accuracy is the only thing you have to worry about here. Go slowly and build up to the 4.3 notes per second you need to get the achievement.
Just going carefully and speeding up once you're consistently getting 64/64, you should be able to get this achievement within a couple tries.