1. How many sound systems had a real 'sub-woofer' of any kind in 1983?
In the 80's it was the age of large speakers with an average driver size of 12", and 15" were common, this made the use of subwoofers limited outside of the pro market. Most subs that would have been available back then were esoteric type of products and passive rather than the current active types. The real audio buffs would have been running older Tannoy's and the like, in the USA it was more JBL and Altec. the 'subwoofer" craze was largely adopted by consumers with the advent of Dolby Digital and 5.1 soundtracks.
2. How many home stereo systems used a bi-amplified setup with four amps, for low/high(s) in 1983?
It was a lot more common to have pre/power setups back then, large transformers and capacitance bank or large receivers able to handle high current output. The bi-wire/bi-amp setups on speakers are a newer thing, a marketing tool when hi-fi started to struggle. In the 70's and early 80's a hi-fi system was generally the third biggest purchase by a household (house/car/hi-fi) by the mid 80's the all in one BPC era had started to take hold and people didn't spend as much on there systems, the marketing departments needed something to draw consumer to their products and the "Bi system" started. Don't get me wrong JVC, Sansui etc all had Bi/Tri terminals on their higher end speakers but it was not on all models in their ranges like today.
I know Panasonic was big into Bi/Tri setups in their all in one systems in the 90's-00's
