[Matt Ion]

wrote:
I would like to power two pairs of 8-ohm speakers with an old Pioneer
SA-8500 II integrated amplifier. The back of the amp reads, "A, B, 4
ohms or more/speaker; A+B, 8 ohms or more/speaker". One set of
speakers will be in the room with the amp and the second pair will be
outdoors. If possible, I would like to control the volume of the
speakers in the room using the amp's volume control and the volume of
the outdoor speakers using a volume control installed in a convenient
location outdoors near the speakers.

Is this doable? Would I connect the speaker pairs as "A" and
"B" and install a volume control on only the outdoor pair? In this
case would I need an impedance-matching volume control? Any help is
appreciated.

All it means is that the A and B outputs are paralleled together (ie. having
both on at once is the same as connecting both sets of speakers to the same
terminals). The amp will handle loads down to four ohms, so if you have only
one set connected (or switched on) at a time, the speakers can be four-ohm
versions, but if you want to run both channels at the same time, the speakers
can't be below eight ohms (two eight-ohm speakers paralleled equals four ohms).

Since the A and B outputs are really the same output, then of course, the amp's
main volume control will affect both; as others have noted, you can add a
separate volume control for the outside speakers, but it will still only turn
them down from wherever the main volume is set.

The only ways to have completely independent volume control of the two speakers
is to use separate amps for each, or to use a multi-zone PA amp.