No, you do not need a discrete sound card. Every motherboard will have 7.1 HD sound.
Try onboard first, you can always add a discrete sound card later.
Some comments on your build:
1. In a new build, go with 4670K. It is 5-7% faster per clock up front.
2. CM hyper212 will come with thermal paste. extra is not needed.
3. Sabretooth motherboards are overpriced. Any Z87 motherboard will do at half the price. Z87 as a haswell chipset has advantages, like more than 2 6gb sata ports.
3. I like the ram pick, 8gb will be fine for just gaming, but ram is cheap so 16gb is probably a good thing.
4. A ssd for the os is fine, but 60gb is just too small. 120gb will hold the os and a handful of games. with 240gb, you may never need a hard drive at all.
Consider deferring on the hard drve, you can easily ad one later. My picks ofa ssd for reliability would be Samsung or intel.
5. 7870 is ok. But, I might look at a GTX660. It is in the same performance tier and cheaper.
Also, the direct exhaust blower cooler will get heat out of your case and keep it cooler.
http://www.newegg.ca/Product/Product.aspx?Item=N82E16814130826
6. I like the case. But, I think you are overdoing it on fans. The supplied fans should do the job. You can always add fans later. And... I would use 140mm fans instead of 120mm; they will be quieter. Don't bother with side fans, they tend to disrupt normal front to back airflow.
7. The corsair 600w psu is a decent budget psu.