...stereo system...has surroundsound outputs...labelled as 16 ohm
...can I use a pair of 8 ohms in parallel ?
James (Coyoteboy)

Not parallel--SERIES.
They must also be phased properly or the sound will be thin.
This should be easy to determine by ear;
swap the polarity of the wires on one of the speakers
on one of the channels and listen.