The soundinfo command prints current sound info to the console ("total channels" is the current number of active channels), setting s_show to 1 and running a server with maxplayers 2 or fewer prints up to 32 sounds on the right hand side of the screen.
Note that there are always 12 active channels from what i can tell, those are special ones.
The first 4 are ambient sounds (seems to be obsolete from Quake, used to be defined in BSPs but never read), then there are 8 dynamic channels. A comment from WinQuake explains this:
0 to MAX_DYNAMIC_CHANNELS-1 = normal entity sounds
MAX_DYNAMIC_CHANNELS to MAX_DYNAMIC_CHANNELS + NUM_AMBIENTS -1 = water, etc
MAX_DYNAMIC_CHANNELS + NUM_AMBIENTS to total_channels = static sounds
It's actually 0 to NUM_AMBIENTS - 1, then NUM_AMBIENTS to MAX_DYNAMIC_CHANNELS + NUM_AMBIENTS - 1, then NUM_AMBIENTS + MAX_DYNAMIC_CHANNELS to total_channels.
ambient_generic plays static sounds, so there are 128 - 12 = 116 static channels available.