you don't need a special coax modem for gaming. whatever you have now is fine. the sound card and Bigfoot nic are a complete waste of money. what's on the board is just as good. a two slot GPU will always obstruct a slot. the 7750 is a very low end card. it only uses 55watts so that PSU is overkill. if you are even thinking about crossfiring 2 that's a waste just get a single 7850 when they come out in a few weeks.
- Almost all decent GPUs are two slots wide, so it will obstruct the next PCI port. Motherboard makers are aware of this and almost always design them so the slot right in front of the main PCIe x16 slot is not anything important.
- You do not need a sound card for almost anything other than heavy-duty sound editing. For gaming, the sound module on your motherboard is fine and an add-on card is a waste of money.
- You do not really need a "gaming network card" either. All they do is give your gaming traffic priority over other network traffic. A much better idea that doesn't cost $100: Just stop any other downloads or turn off any other devices that would be hogging your bandwidth.
- The Motorola SurfBoard is a fine cable modem; I have one myself. They do also make one that's just a modem, not a modem-and-router in one, and getting a separate modem and router is not any more expensive. Personally, I'd get them separately in case a) one or the other breaks, you don't have to replace both, b) they come out with something better than 802.11n wireless before you're done with that modem, or c) you find yourself not needing a router one day.
- You have two different video card on there right now. I'm assuming the HD 6790 is the one you meant. For crossfire, you really only want to crossfire with another of the same card. Two HD 6850s does pretty well for the price right now, but don't crossfire just to crossfire; see if a single card can do the same job. Less complicated, causes fewer issues, and usually uses less power.
- Usually, a $200 case is unnecessary. That one is a better value than most for the money and Antec tends to make good cases, but really ask yourself if you need it.
- I'd do more research on CPUs, personally. The new AMD Zambezi series was pretty disappointing. People will probably tell you the Intel i5-2500k is by far the best value for the money unless you're on an extremely tight budget, which it doesn't look like you are. They'd be right. This will also affect your motherboard.
- Way too much RAM. You do not need 16GB unless you're doing professional photo/video editing. For gaming, half that is still more than enough.