I don't think that a sound card will make a difference with a headset like it would with a set of speakers. My motherboard has a Creative X-FY chip on it for thx and dolby digital sound. I also have the Bose speaker system that connects to the Pc by usb so it gives me two different sound options. In my headset I notice no difference between the two.
Todays motherboards are not like the old ones that needed a sound card to get sound , these MB'S today have high definition sound chips intergrated right on the board. The highend boards even have highend chips on the board like the Gigabyte G1 Assassin I have has the Creative Labs Soundblaster X-FI.
these MB'S today have high definition sound chips intergrated right on the board.
But it is much more difficult to to design noise/crosstalk-free on-board audio on a motherboard where the HDA chip is surrounded by high-power traces and tons of digital signals spanning multiple PCB layers than it is to do the same on a dedicated audio card where the ADC/DAC has its own dedicated PCB island with only the solid analog ground and power planes buried under it.
Lots of motherboards have significant noise/crosstalk issues on their analog outputs, often reported as hearing noise while moving the mouse or while HDDs or other intermittently active devices are used/accessed. This type of problem is not as bad as it used to be with AC97 but it still exists.