I havn't seen a wall box with speakers in it, but that doesn't mean there aren't any.
Your picture shows the amp, and the wires connected to it should go to the output xfmr.
The output for the external speakers should be around 4" x 6", have multiple connections
for the output level you want, labeled 1-5, 1 being the lowest max output, 5 the highest.
The wires on the amp should go to the output xfmr, follow those and you should find it.
Attached is a jpg showing the 200w amp (top) and output xfmr (bottom), this should give
you an idea what to look for.
Hope this helps!