Rockwood is crap. They use the Name to try and confuse the uniformed consumer into thinking it's Rockfor-Fosgate, just like they use the XPlor line to confuse the uninformed consumer into thinking it's Sony XPlod (not all that great either, but highly advertised).
At least those Punch subs aren't the paper cone crap they sell!
If you have a decent OEM stereo and want to add a little tight Bass to it, but are on a budget, the best way to go is to add a nice 10" sub, like a JL W0 in a sealed box and a decent small amp to drive it. The are SQ and SPL fanatics that will tell you that you need $2000 systems to start with, but what you want and need is what really matters.
There are alot of lesser known amp brands, and weeding through them is confusing. Many of the well known audio brands, such as Kenwood, Pioneer, JBL, Power Accoustics, Clarion, Panasonic, Phillips, and others use Sound Around as the manufacturer of their amps, confusing things even more.
Go to the Web Site of the manufacturers and compare the specs. If you don't have pre-outs on your head unit, you'll need an amp that has speaker level inputs. RMS power should be given with all channels driven. If it's a class AB amp, THD should be under 0.05% at rated RMS power. Signal to Noise ratio should be >90db at rated RMS power. It is important that they specify these at rated RMS power. If they don't give these specs, consider them to be crap, they are obviously embarased to publish the specs. Look for a 2 channel amp that can be bridged ( most can ). While THD is less important for a sub amp, this helps give you an idea of the quality of the amp. Class D amps are more efficient and mono amps made expressly for driving a sub offer great power, but don't expect the specs to match those of a AB amp.
If you buy a major brand, you will pay for the name, MTX and RF amps are nice, but over priced.
HiFonics, USAccoustics, Phoenix Gold, and Precision Power make some nice mid-level amps in my opinion.
my 2 cents worth, I hope this helps