Chess, the first point is that a single amp could theoretically drive dozens of speakers if they were connected in a series and parallel combination so as to keep the overall impedance within normal limits. In the case of the 3802 the two side surround amps can each drive two surround speakers simultaneously when A + B is set because those speakers are driven in parallel(e.g. if they're 8 ohms the resulting impedance is 4 ohms). So certainly, 9 speakers can be powered, but this isn't anything unusual. Even a 7 channel receiver which doesn't have the A and B side surround terminals can be hooked up to 4 side surround speakers with the appropriate wiring scheme. Of course, the receiver in that case wouldn't have an internal provision for selecting A, B or A + B.
