Nah, thats not possible in Source engine. Since source cant recognise between indoor/outdoor. And for this mod, there is one sound but Dualchannel used. Each channel is for each situation. Left channel is for short distance, and right channel is sound for long distance.
Edited scripts. This has nothing with CSGO. I wanted to make it like CSGO but it doesnt work in CSS. Just distance sounds are from CS:GO. Script values are from DoD:S/L4D2/HL2 where left channel of the sound is used for short distance, and right channel is used for far distance.
Extract zip file into your Cs source folder. Example: C:/Program Files(x86)/Steam/SteamApps/Common/Counter-Strike:Source/ Zip file contains: cstrike/custom/my_custom_stuff/scripts And cstrike/custom/my_custom_stuff/sound