It is possible to stack in between those two and do a full asura combo

Question 2: Can combo asura damage reaches Bounty Bay gold the same amour of the Manuel asura damage?

Answer: The combo asura damage is about half of the Manuel asura damage, it is hard to reach the same amount of damage as the Manuel.

But think again, you use chain crush and stuffs that deal damage; the combined damage is almost the same as the Manuel asura damage.

But if you really not confident to take down a high HP monster (example Maya purple) with 1 or 2 combo asuras, try combo 3-4 times using the chain crush combo and proceed to asura combo as long as you pump your SP to the max.

Question 3: The guide book of the official server says tiger knuckle fist cannot be cast in between way of dragon and chain crush combo, is it true?

Answer: For this I can say it is definably not true, probably some official servers don allow it or something like that, it is possible to stack in between those two and do a full asura combo from it, as you have 1 sphere left after chain crush is casted.

It is also possible to revise the combo by adding another tiger knuckle fist after doing the whole process as long as you have 1 sprit sphere around.