Two ways:
1) Source -> pre-amp -> amp -> V-2 speaker input
and Source -> pre-amp -> amp -> SA-1 speaker level input
So you basically come off of the speaker input at the V-2 and run jumpers over to the SA-1 amp, or Y the output from the amp with one pair of speaker cables going to the speakers and one pair going to the SA-1 amps.
2) Source -> pre-amp -> amp -> V-2 speaker input
and Source -> pre-amp -> SA-1 using low level input (RCA's).