TS-653B : which 8GB (2*4GB) set to use?

[Maccied0891]

This question has probably bin asked before, so I'm sorry for repeating it again.

I own a TS-653B with 4GB RAM (2 * 2GB)
Now I would like to change the memory to 8GB (2 * 4GB) , thing is : which memory set should I buy ??

QNAP use to have a 8GB, 2*4 set for sale on their website for a TS-653B, but it disappeared ?
(And ofcourse I didn't write down the serial/production number)

My main concern is that the set has to work straight out of the box, no weird crashes or anything.
Because of my work I just don't have the time left to tinker with hardware now a days.

And I use the NAS alot, so I have to be sure that it functions without hickups.