I dunno if this will helps for you, but i had the same issue with these throw combos like 5K > JK iad JKPH. I was doing it like (5K) then hold my stick to (9) and press k as soon as i saw the jump and then do IAD etc. which was totally tigh but possible. (So i don't recommend practise this! xD)
It takes a while until i realize (and it makes click in my head) you have to buffer the jump, the buffer for these throw combos feels more like an JumpCancel or Jump Install. So throw > 5K > JumpCancel > jk > JumpCancel > IAD > JKPH.
After i got this, the throw combo was much easier ^-^