even if you could fit a sound card in with 2 videocards its going to restrict the airflow and generate more heat to deal with. at least with my video card it can get up to 80*c unless i have the fans cranked up to 80+%.
Newegg.com - VisionTek 900250 Radeon HD 4870 X2 2GB 512-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Desktop Graphics / Video Cards
thats my videocard, i have sapphire brand but its the same hardware pretty much, newegg just doesnt sell the sapphire version of that anymore. if you look at the pics it takes up 2 slots and is pretty long so airflow can be a struggle when the actual hardware takes up that much space. 95% of my computer problems since i built this rig have just been heat issues, i turn the fans down to like 40% when i go to bed so its nice and quiet and if i wake up and start cod4 or something without turning the fans back up it can overheat.
anyway i have been makin my own computers for about 6 or 7 years, built 4 different rigs and never had a separate sound card. evga 780i or 790i have really nice built in sound, you can have hdmi hookups, regular hookups or even just use usb to plug your headphones in and it all sounds perfect to me. im not really an audiophile though, i just use a 5 speaker+subwoofer setup from bestbuy that cost me like 60 bucks.
edit: i forgot to mention that you can setup programs to handle you video card fan speeds based on its temperatures. for example you can have it at 40% minimum speed, and then every 5 degrees the temp increase you can make the fan 5% faster. im just lazy and find that i would rather just control it myself even if i do forget sometimes.