My old Sansui did the same thing. I placed a couple high wattage resistors in the second set of speaker outs (B). My speakers are on "A". When I'm ready to turn it off, I lower the volume, switch to the "B" speakers that have the resistors and turn it off. The resistors take the load. No pop. When I'm ready to listen again, I switch it to the "A" system and I'm set.
If you do this, be sure the resistors do not contact anything to short out. Place something on the leads if you need to.
If you do this, be sure the resistors do not contact anything to short out. Place something on the leads if you need to.