Espero que isso faça você começar (note que o modo profissional seria conectar-se ao link ):
#!/usr/bin/python
import subprocess
output = subprocess.check_output("pacmd list-sinks".split())
on_active_sink = False
i_want_as_db = False
for index, line in enumerate(output.splitlines()):
line = line.split()
if ['*', 'index:'] == line[:2]:
on_active_sink = True
continue
if on_active_sink and 'volume:' == line[0]:
if not i_want_as_db:
print line[2]
break
else:
print output.splitlines()[index + 1].split()[1]
break