It doesnt do much at all to splice speaker cables. Even just twisting them together will give plenty of connectivity. The cables on that system should be like 6 ft. for the front and center, 10 ft. for the sides, and 16ft. for the surrounds... maybe more. The cables are skinny little things, and connected with jacks that fit "RCA" or stereo jacks. You know... connector on the outside, and a thick pin in the middle.
I have the P7800 and it works prety well. The sub is quite loud and powerfull for such a small system. Review at http://www.xhardwarereviews.com/p7800.php
The sub can go next to your monitor, but:
1. It looks weird
2. It takes up space
3. Doesnt give you quite as much sound
4. May screw up your monitor
I would put the sub in the corner under your desk as far as possible, such an area will give you TONS of bass, even with carpet.