# Left channel
# This will match output ports of any client named 'out_1', 'out_l', 'output_1' or 'output_l'
.*:out(put)?_(1|l)$
    system:playback_1

# Right channel
# This will match output ports of any client named 'out_2', 'out_r', 'output_2' or 'output_r'
.*:out(put)?_(2|r)$
    system:playback_2

# Another common naming scheme for output ports:
.*:Out L
    system:playback_1

.*:Out R
    system:playback_2