If you have a decent deck it'll probably be sufficient to power a set of tweeters. They're small and therefore don't draw as much power. My stereo in my truck is full JL Audio and im quite satisfied with it, and yes my tweeters are ran off of my deck, and seem to work just fine.
If you have subs that big, with that much power, i would get something to fill in the mids and highs with. You will probably need to balance everything out. I would find a decent crossover and use an amp for mids and highs. That way you can adjust the settings to make the sounds that you need.
the only way u need to run and amp to your system is if your pushing like 4 15's and cant hear shit but rattling i have had my 15's kicker comp vrs for like 2 years and ive had them installed w a shitty durabrand deck??? and also a sony dvd touch screen ( in the process of installing in tha 9c1 right now ) and if u have good tweeters or 6x9s or whatever u will get enough power from your deck to hear words etc fine but it looks better if u have the 2 amps set up nice when u do have it installed also u will have to buy a double amp wiring kit for the second amp, which isnt very expensive like $40 at walmart and its pretty good quality:biggrin: