most 7.1 headsets come with a soundcard of their own or are usb with it built in to the headset. the vast majority of surround sound headsests are virtual surround so do not need any fancy soundcard to work.
the only reason you would need a 5.1 or 7.1 analog output soundcard is if you plan on purchasing an analog 5.1/7.1 headset and do not want to use any included soundcard solution.
otherwise, the only reason for buying a soundcard would be for providing virtual surround to a 2.0 set of headphones or a 2.0 headset. razer virtual surround software is free and will give you the option without spending any cash. if you wanted a hardware solution, the xonar u3 is small yet offers dolby headphone if virtual surround is what you want.