Depends on what you want to accomplish with the wax. If you just want to give your paint a bit more depth and wetness then you should feel free to top SG with whatever non-cleaner wax you want (Natty's Blue, Meg's 16, Souveran, etc...). SG by itself is a pretty durable product, especially when layered, so adding a wax on top of it won't really effect the length of protection it provides.