Will the Klipsch Promedia 5.1 system be adequate for my home theatre?

I posted this message in another forum, but I figured you guys may have much more insight on the topic, so I'm pasting here ;). Since this is a DIY audio forum, I just need to include my personal abilities. I do have a strong understanding of electronics, have taken some electronics courses, feel comfortable with Ohms law, RLC circuits, and have done some soldering before. With that said, I don't really want to have to pull out my old electrical engineering book and spend weeks making an amp that will only save me a few bucks. If the savings is unbelievable, the schematics are complete and readily available, and it won't take me a week to solder everything together, I might entertain a few DIY parts in my audio system though.

I am currently in the process of building an LCD projector to function as a home theatre. While I have no end product yet, I am very confident that my results will be good enough to get a 200" high definition screen to look good even during the day.

What I need now is an audio system that will function adequately in my up and coming home theatre. The room I have is about 20 feet deep and 15 feet wide. I will have a pull-down screen being used so most people would be sitting on the couch about 15 feet from the screen. As I am a computer geek, I will, obviously, be using a HTPC to run all media.

Currently, there is a deal on the Klipsch Promedia Ultra 5.1 system that would allow me to get a set of these speakers delivered to my door for just a bit under $300. As that is still a rather hefty price tag for me, I want to make sure that I don't have any better or lower cost alternatives. As the speakers will be powered by a computer and the Klipsch speakers are the best computer speakers in the market, this seems like a no brainer but I just need to be sure. Soo..here's my questions:

Can I find a similar cost, higher output, reasonable quality 5.1 - 7.2 speaker setup that would work with an Audigy 2? If so, where should I start looking and what should I be looking for? Aside from amplifiers and speakers, what else is essential to merge home audio equipment with a personal computer?

And, of course, if I do decide to buy these Klipsch speakers, would they be powerful enough to give the room a commanding audio presence? I have heard the 4.1 speakers in action before, but this was in a small computer room. I am afraid that the Klipsch speakers will be rather unimpressive when used in a larger room.