The A50 takes optical input only, or 3.5mm analogue. Using the 3.5mm will bypass the DAC of the A50 and use your onboard sound which probably sux. It just adds wireless and a headphone amp to your onboard sound. Using optical takes advantage of the DAC and dolby headphone virtual surround sound of the A50.
I'd recommend a USB DAC that adds an optical out. Something like the M-Audio Super DAC for $150. You could use the optical out from that to feed your A50 headset. That USB DAC can also feed a regular pair of studio headphones. So any nice pair of AKG, Seinheisser, etc.... for under $200 will blow your A50 out of the water. And a regular pair of studio headphones should last forever as they have easily replaceable parts. They also do double duty for music, stereo system, cell phone, mp3 player, guitar, etc...
Now what your missing using the USB DAC is the virtual surround sound for games. The only way to get surround sound for games is to use a headset with 3 speakers in each side which is great for games, not so great for music. Or to use virtual surround sound which is not bad for games, and turned off great for music. A sound card comes with the software to do this and that's the difference between just a DAC and a soundcard. A soundcard is a cheap DAC + software. Your A50 headset is an external DAC + Dolby software. The M-Audio super DAC is DAC only. You need a program to give you virtual surround sound. Creatives offering and Dolby is not available as a stand alone program. Razer however offers a free Razer Surround as a stand alone product for free. Run that and use the Super DAC in games for virtual surround sound. However using the optical out with your A50 you don't need the software. But lets say your A50's break.....you just need a regular pair of headphones on the cheap and plug into the super DAC.
What the regular headphones don't have though is a microphone. That ok. Go get a YETI or Blue snowball and get better audio than any headset. And you don't have a microphone hanging off a pair of headphones in your face and in your mouth. Or if you have a webcam just use it's built in microphone and problem solved.
My recommendation is to get a USB DAC with Optical out like the M-Audio. Use your A50's for now. When they stop working get a regular pair of headphones and use the Super DAC. Or take the money of the super DAC and replace your motherboard. But if you get a new motherboard, the day your A50's break you're left with nothing. At least with the super dac you have the option of always buying a cheap motherboard in the future and will never have to worry about audio problems.
FYI most people are claiming that Dolby headphone isn't that great. They say Razer Surround is better. And it's free or just $20 to unlock all it's features.