haven't seen a retro sound radio in person, but another option is to mount an aftermarket in the dash and have the stock one in the main hole if that is what your looking for. They also have adapters that plug in between the antenna plug that give you an option for aux/ipod hook up, just fyi.
as for harder hitting sub, you would be better off making the box ported if it is not already and it is the easiest option. Sealed boxes give you cleaner more precise hits, but a ported box will be louder (also you can not just drill a hole in it to make it ported (unless you buy a port tube and have room for it), you have to make sure it has enough area inside and most subs recommended the best style of port to go with the box). It also depends on how your sub and amp are match, you should always look for the RMS watt ratings and have them be similar ratings. Also is the sub amp a 4,2, or mono channel amp?? does your sub support 8,4,2 ohm? The low the ohm you can run the harder the hits will be.