DIY Sub upgrade for cheap 2.1 setup

Just bought a cheap 2.1 setup, the Eagle Tech ET-AR306-BK
.
(http://www.eagletechusa.com/ET-AR306-BK.htm) and the sound is meh, but for 50 bucks I can't complain too much.

The speakers are so so, but the subwoofer is downright shameful. I was thinking what might be fun is a little DIY project where I rebuilt the subwoofer in this little guy.

It's a 5" sub with that takes 15 Watts RMS x 1 (into 4 ohms, @<=1% THD). Did some googling and found this guy:



Pyramid PW577X 5-Inch 200 Watt Subwoofer (http://www.amazon.com/Pyramid-PW577X-5-Inch-Watt-Subwoofer/dp/B00069QV5I)

The resistance matches, but I have a feeling that if I hook up this sub to the existing little cheap little 15Watt Mosfet amplifier circuit, I'm gonna be dissapointed.

So then the question is, if I need to re-amp this thing, what would be a good way of doing this, cheaply? I could pull off the existing amplifying circuit inside the sub and re-wire it to another, better more powerful amp, but I'm not sure what would be a good choice. The sub above can take 200 W peak, 100W RMS, but I feel like I'd rip the enclosure apart if I did that. This thing is still pretty cheap. I was thinking maybe get a cheaper 50W rms single channel amp and use that. Any suggestions?

Also, would it be best to replace the existing 15W amplifying circuit completely? Or would it be possible to actually take the amp'd output from that and then route that into another amplifier?

I've never done any of this, so any suggestions would be appreciated.

Below is a pic of the printed circuit board within the 2.1 setup above:

Found this guy a 2x50W amplifier kit that would be perfect if I bridged the outputs: http://www.aliexpress.com/item/50W-50W-LM4766-Amplifier-kit-sc/654096728.html

That being said, I'd need to re-wire in another transformer to support 100W @ 24VAC ... aka, 4.17amps ... Dang, transformers are expensive! - http://www.amazon.com/SECO-LARM-ST-UVDA-W100Q-Transformer-24-28-100VA/dp/B0051BU27Y/ref=sr_1_2?ie=UTF8&qid=1349730122&sr=8-2&keywords=120+vac+transformer+100va

Bump for answers! Also, I get the feeling my 'build' might be on the low end compared to what you guys normally discuss. If so, any suggestions for other forums that might be able to help me out in this?

Don't get me wrong, I fully realize that my proposal is FAR from cost or time effective.

I was just thinking this would be something fun to waste some time on. I chose cheap parts because I'm doing this all for funsies without getting too serious about it. If I wanted to take that approach, I'd probably go for building my own enclosure too, and drastically better hardware.

But for the time being, it's more of a "let's throw a couple bucks down, get out the soldering iron and do something new".

So, I'm really just asking all of the above to see if what I'm thinking even makes sense.