As far as I'm aware Matthew, there is no way to convert your Amex Rewards points into QFF.
You can transfer your Amex Rewards into a range of other frequent flyer programs, Virgin Australia, Singapore Airlines Krisflyer, Etihad and Cathay Pacific's Asia Miles. Asia Miles is a very good program to accumulate miles in where you can, but this is usually done by flying or transferring points into their program.
I've had a quick look on Asia Miles and they require 40,000 miles for a one-way economy award from Syd-Honolulu or vice versa with Qantas or American Airlines. AMEX Reward Points transfer 1:1 into Asia Miles, so if you used your David Jones card until you reached 40,000 AMEX Rewards points, you could then transfer to Asia Miles, and have 40,000 Asia Miles points. At a quick glance, there are hardly any award seats available though, PLUS it's difficult to see what the taxes and charges would be (I believe they can be quite high, similar to what Qantas charge).
The 60,000 QFF points are enough to get you a return trip to Hawaii with Jetstar through the QFF webiste (you'd have to look carefully for Jetstar only award flights. If you choose any segment of the journey, for example, Syd-Brisbane, on a Qantas leg, the amount of miles required will increase above your 60,000). Hopefully by the time you get the 60,000 points though, you'll have incurred some more spend and more points anyway. While there is plenty of award availability through Jetstar on there, the problem is Qantas' taxes and fees. So while you can get a return direct trip to Hawaii through QFF website on Jetstar planes for 60,000 QFF points, the taxes and fees charged by Qantas are around $470!!
I've just had a quick look and Jetstar (on their own website) are offering plenty of DIRECT return flights in September to Hawaii from Sydney for $573 return (including taxes). For that price, I'd be looking to book with Jetstar, pay cash and hold onto those 60,000 points. It's an excellent price.
You'll see from searching around the QFF and Jetstar websites that those 60,000 QFF miles will only save you around $100 at the moment (while those Jetstar flights are on sale to Hawaii). That would be a waste. Plus, most of the award flights on QFF website fly on Jetstar but make you fly via Melbourne or Brisbane on the way there and back (I'm assuming for some reason that you are in Sydney. If you're in Melbourne or Brisbane, than it's not so bad).
At this stage, my advice would be to hold your AMEX points in the AMEX rewards program, and hold onto your QFF points when they arrive.
A challenge with the whole points hack thing is having points spread over different programs, and this can be frustrating at times. There is plenty of info on this site about the various programs and approaches to points. If you are in a position to snap up one of those Jetstar direct return fares to Honolulu in September for $573, I'd be doing that. If you decide to go for that option, don't forget to use POLi to pay for your flight so you avoid Jetstar's booking fee!
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If you have any more questions about the above, ask away...