Are you thinkin about running components in your front AND rear? Imaging is going to be pretty difficult, not mention it could potentially get expensive as far equipment goes... If not, then why go 5-channel? Unless, you're going for an active setup, there really is no point to it.
Instead, you should consider a quality 4-channel. A la..
http://cgi.ebay.com/ebaymotors/ws/eB...RK%3AMEWA%3AIT
You can run 80x2 @ 4 ohm to your components up front and 320x1 @ 4 ohm to your sub(s). All ratings @ 12V (unlike newer Alpine amps..) My buddy just has his PCX-480 benched and apparently, it did 523 x 2 @ 4 ohm... I'm not sure what this translates into 4 channels, but I imagine it being a lot...
If you're on a stricter budget, you might want to consider a HiFonics ZX6400. They can had in the sub-$200 range and they are great budget answers.
What components and sub are you looking to run?? Is you heart set on JL or would you consider other options?