Sounds like a nice wiring setup. I would love to have a conduit/crawlspace to run everything through, but everything here is built on a concrete slab.
Anyway, sounds like we have several options here. Your original idea of using a 5x8 multiswitch will certainly work, but let me point out a couple issues. First, do you really want/need 8 separate satellite receivers? That can get a little expensive, and if you only have 4 people in the house (for example), then at most you would only ever need to tune in 4 separate channels. Also, if you ever get a taste of a Tivo/Ultimate TV system, you will never go back, and those systems require 2 satellite feeds each (they have 2 tuners), so that would use up your cables pretty quickly.
I have just moved and finished wiring my 2nd house for this stuff, so let me just tell you what I did, and what I changed the second time around, just to give you some ideas. As you start to figure out what you want to do, feel free to ask more questions and we'll help you figure out the best way to accomplish your goals.
My first house was wired very similar to yours - I had 2 RG6 cables run from each room to the headend, which was in a closet in the study. I also had 2 RG6 cables ran from the attic to each primary living area (family room and game room), and in the attic had a 3x4 multiswitch to connect them to the dish. The other RG6 runs were used in a classic upstream/downstream configuration. The family room and game room each had 2 modulators (2 SAT receivers, DVD, VCR), connected to the upstream cable. These upstream cables were mixed with regular cable TV at the headend and fed into a distribution unit, which then fed the signal out to all the rooms over the downstream cable. I chose the distribution unit because it had integrated infrared support and some nice wallplates for each room that made for a very clean installation. You can certainly do the headend yourself without a prebuilt unit, but with the IR you have to be sure to bypass any amps in your system, and it sounded like a PITA.
When we moved, I changed things around a bit. First of all, it wasn't a new house this time, so I couldn't get in and prewire anything. Luckily, it's a 1 story house, so I have attic access to most of the house and was able to run cabling to the couple rooms that needed it. I also made the decision to put all the AV equipment in the family room this time. Main reason for this is that I wanted the best connection from all the AV components to my home theater system. Before, if I wanted to view the upstairs satellite receiver in the family room (which always happened, because the kids had all their stuff on the main unit

), it was going through the modulator, so no stereo, lower quality video, etc. With the new setup, I no longer have that problem. Also, having all the components in one area simplified things a lot - I run outputs from everything to a 4 channel modulator right there in the living room, and then run the modulator output back up the wall and split it between the other rooms. It's very easy and straightforward, and this time around the whole setup only cost me around $350.
BTW - I had my last house wired for audio too, and never got around to setting it up, due to the cost. For the current house, I just put the CD changer on an extra modulator channel - not perfect, but it's good enough for listening to a CD while on the treadmill, etc., and it only cost me $40.