Powerwax can be layered. Synwax is a lot like Meg's NXT, it has light cleaners but it can still be layered. Just dont use too much pressure.
Quote regarding FX Synwax from waxforum.com by Alfisti:
I have time I prefer to apply the second layer a day or two after - giving time for each layer to cure. In my experience, you can layer two coats, with each coat adding to the previous, if given time to cure. The difference is very observable. The mild cleaners may take some of the previous layer off, but not much. The more gently you apply the second coat, the less it removes from the previous one. So two coats 24hrs apart may provide 1 3/4 layers, which is much nicer looking than just one layer. Try it...you'll see what I mean...your eyes will water.