Is there a way to use sendkeys (or something equivalent) from (not to) the command prompt?
You can use vbscript. For example, this script will mute the speakers.
set shell = CreateObject("WScript.Shell")
shell.run"Sndvol"
WScript.Sleep 1500
shell.SendKeys"{TAB}"
shell.SendKeys" "
shell.SendKeys"%{F4}"
You launch it from the console with
cscript mute.vbs