Adding to the chorus: lots of options, something you'll have to compare and decide on.
Malaysia fly to Istanbul. Awards can also be booked onto the Turkish airlines codeshare. Would cost about 200,000 points for the flights, which makes it more comfortable to swallow the taxes that are comparable to Singapore and a few other airlines. And plenty to spare on a hotel stay if you wish.
As has been mentioned, look at what airlines you have to choose from, sign up (free) for their frequent flyer schemes and then search for award flight availability first. Once you've decided, then transfer the appropriate points. At least look at the options you can directly transfer to: Thai, Singapore,
Etihad,
Virgin Australia (via
Etihad) etc.
I really couldn't imagine burning a whole 600K on just two return flights in J. There is a lot better value out there. Best example: Transfer to Asia Miles (Cathay Pacific) and a multi-carrier/alliance award would cost 440K for two to travel business up to 50,000 miles (approximately twice around the world). These are complicated and much more than you need, but my point is the actual value between available options varies greatly.
All the above carriers transfer 1:1 from your Amex account. Otherwise as has been mentioned you can transfer to SPG and then through many other airlines, including the US ones. This is a trade off here is possible more points / less cash, depending on your circumstances.
Don't think first class isn't an option either. Look at each direction separately, no need to book them return through the same carrier.