Check what's the price after including shipping, as Amazon can be really expensive. There's one option you can go, check out CDJapan, bought my IM50 there, and many many KPOP CDs.

Amazon will include total cost inclusive of import fee and also shipping together with your order. Another to note is whether they will ship the particular headphone to Malaysia as Amazaon have restriction on shipping to M'sia

I looked through ebay and the price for AD900X ranged about RM700 (including shipping and import charges) and above. I think the RM500+ ones are AD700X? Amazon does sell them cheaper but it seems the shipping handling and import charges aren't calculated as well. And only one listing does ship to Malaysia, that one is USD149 which is about RM66+. Not sure how much is the shipping and import charges to Malaysia, but it should add at least RM150 into the price.

I'd suggest getting locally since the warranty will be easier.

If you're really interested to get the best sound, I'd suggest you test both of them out and before making a decision. It pays to buy the best pair by saving instead of buying the cheaper model with the intention to upgrade.
However if you don't intend to upgrade, the AD500X would suit you better. As always its up to you.

For Amazon order, it will not incurred any more cost coming to Malaysia as you have paid upfront. If the custom tax is more than what you paid, Amazon will pay the difference