David, I think the box you speak of is just the sub-woofer, which on ours is in the middle cabinet under the dinette/buffet.
For many coaches of our era, Bill, the amplifier was part of a DVD/CD changer unit. When your previous owner switched to a modern digital-tunered TV, he likely tossed that unit as, similar to our Sony removed by Jim Sizemore (RV Outfitters), amps back then lacked HDMI ports. Exactly what amp might have replaced yours is hard to say, but shouldn't be too far from the cabinet Jeff refers to, since all the Bose speaker wires terminate there.
After some research, I had Jim put in a Sony BDV-E3100 blue-Ray home theater, but just the main unit. The amp is part of that new Sony blue-Ray home theater unit. The speakers that came with it I store for some possible other use at home since the existing Bose ones are fine; nothing was to be gained from the added cost of such a speaker retrofit. I may use the Sony speakers in a room at home together with one of the old analog TVs and DVD/CD player.
So I'd expect you need to fish through the snake pit in the overhead VCR cabinet for your elusive wires. They could have been stuffed way back behind, in the void between there and the front cap.
Joel