I completely agree that if you're using the HU to power the speakers, you should be getting coaxials instead of components.
I'm also VERY skeptical of generic speakers using such names as "SPL". There are actually plenty of 'cheap' ones out there that aren't half bad, they are just made like old school stuff rather than the latest and greatest from more expensive manufacturers. But there is also a lot of pure garbage that is made cheap, cheap, cheap that looks flashy but in reality is poor quality stuff that works just long enough for you to lose the paperwork or the seller to close up shop.
I'd say you're better off with 6x8's, either 2-way or 3-way, something like Pioneer, Kenwood, etc. Even some cheesy JVCs to match might work. Walmart sells the Pioneer 6x8's for $59.99/pair, but you could also get some less expensive 6.5" coaxials and use adapter plates.
If you're looking for deals I'd say stick to either finding brand name sale/clearance stuff at audio shops, or major websites. Some people have good experience with audio equipment on ebay, but from what I've seen, most of the 'too good to be true' stuff is either cheap junk or refurbished but sold as new.
If you really want to try them though, I suppose you could get one set, replace the two blown speakers with them, (moving the components to the front), and if they do what you want, buy a second set. It's free shipping so you don't pay anything extra doing it that way, but you lose less if you can't return them once they're used.