you have a kick *** air cooling setup. im sure quieting down some of your fans will give you much quieter performance, and your cooling ability will probably be the same as if you went with one of those external units. i really dont think you should rule out putting together your own components internally. unless you have hard drives coming out of your ears, and have packed in as many pci cards as possible, there is probably a lot of room inside.
edit: i see your tv tuner, sound card, and 2 hard drives. hmmm, the space under your video card is taken, but there must be room in there. i just dont think you'll be pleased with the performance of on of those external units, especially coming from an sp-97