Dig might be able to stop Pain Split when I'm faster than you, but when you're faster than me, it's not a threat, so you didn't need to sub for it.
The real threat is to your Pain Split is Protective/Evasive moves, ie Protect.
I still maintain that using Protect ordering first is a bad idea because it gives me a free action to set up on you.
Right now, your "IF Dig Earthquake -> Substitute -> Pain Split" is pretty unclear. Try formatting it as something like: "IF Protect, THEN Substitute 15 that action and push back future actions." (Pushing back actions means to do the action you wrote for A1 on A2, A2 on A3 and so on, so if I protected A1, you'd use a substitute on A1 and Pain Split on A2).
Also, Substitute needs to specify an amount in ASB. It can create a 15, 20, or 25 HP substitute.
If you're ever curious about how a move or ability works in ASB, you should check in the IRC channel or consult the NDA
here.
Protect | Belly Drum | Play Rough
PS: Belly Drum isn't as good here as it is in-game. But it's still fun.