Enter each of these commands in-game and then restart your client.

/console SoundMemoryCache 128
/console SoundMaxHardwareChannels 128
/console SoundSoftwareChannels 128

put compatibility option to XP SP3 if you get sound issues

You can add this one if you want too:

/console SoundMixRate 48000

Set in game:

/run SetCVar("Sound_NumChannels",128)

Confirm its done:

/dump GetCVar("Sound_NumChannels")

You can add 2 lines to your config.wtf - that way you dont need a modified .exe - the lines to add are SET SoundMaxHardwareChannels “256” and “SET SoundSoftwareChannels “256” - change the number 256 to the channels you want. I have it set to the max of 256.