[old_tv_nut]

You mixed a few issues together, I think.
To do stereo, you need two separate channels. So for good stereo, the first thing you need to accomplish is a good single channel; then you can duplicate it to have two.

So then, you need to create a design for a good single channel, which involves what is the frequency response of the transmission channel and amplifiers (which will carry all frequencies of interest), and then the frequency response of the loudspeaker and output amplifier(s). At this final stage, the speaker can be a single speaker, or a 2-way, or a 3-way (or more); e.g., a 3-way with woofer (bass), mid-range "squalker," and tweeter (treble). The final amplifier can be a single one that drives a speaker with one, two, or three parts, or it can be split into 2 or 3 amplifiers, each of which is optimized for the frequency range of the loudspeaker part it is driving.

In systems with a subwoofer for the very lowest frequencies, the subwoofer often is combined with its own built in amplifier and adjustable "crossover" (electronic filter) to select only the frequencies that the subwoofer is good for.

A (monaural) TV set or table radio or even many early console radios would typically have a single amplifier and a single "full range" cone loudspeaker to handle all the sound. It is much more difficult to get the fullest range of sound frequency output from a single speaker, so HiFi speakers typically are three way or two way. Even with 2-way or 3-way speakers, a single wide-range amplifier is common. If separate amplifiers for each frequency band are used for a 3-way speaker, it is referrred to as "tri-amp."

Hope I am understanding your questions, and that this helps clarify.