--navigate to
C:\Program Files (x86)\Steam\steamapps\common\Counter-Strike Source\cstrike\cfg
--open up config.cfg with notepad and look for windows_speaker_config
this thread says:
"windows_speaker_config 1 NOTES: Allowed values: -1 / 1 / 3 / 4 / 6 -1: Default (2 Speakers) 1: Headphones 3: 4 Speakers 4: 2 Speakers 6: 5.1 Surround"
--either modify the config.cfg file directly (copy and paste a version before you modify it just in case something gets screwed up) or make a new .cfg file in the \cstrike\cfg folder titled autoexec.cfg and add windows_speaker_config "x" x being the number you want as seen from above and save it.
--the commands in the autoexec.cfg folder will get sent to the game every time it is launched. this is preferred over messing with the config file, i believe.
--make sure when saving the file in notepad to file>save as>save as type:All Files and then add the .cfg to the end of the file name replacing .txt. make sure you don't end up with autoexec.cfg.txt. that won't do anything for you.
As your leader i will not force you to give up relationships and play cs instead, that's on you. if i gotta push you to play the game u want to make a living out of, then this shit aint for you.