you will often read that a sub or amp has 90000000 watts, this is normally the peak output, this is a crappy way of judging things as the peak is very rarely reached. RMS is Route Mean Square which is basically the average i.e. the way it will play most of the time. Thats why it is important to match things up by the RMS watts value.
Wiring subs together starts to complicate things a little as you can then change the resistance (commonly know as the "load") shown to the amplifier. The less resistance shown to the amplifier the more power it can throw out, but this means it is workign harder and not all amps are compatable with this. If you decide to wire the two subs together find out if they are dual voice coil or single coil. Then find out what Ohm rating they have, then you will have to look at how the two can be wired together and what end load they will show, the rockford fosgate wbesite has a fantastic diagram bit and shows you loads of ways of wiring with different resistance ratings etc... then you need to look at your choice of amps to see if they can take this load and what power they give.
Alternatively give the caraudiodirect chaps an email or ring them, they are very helpful.
It sounds long winded and complicated once you get your head round it and it makes sense its very easy and understandable
