"
Here is what I don't understand. If I try to play a small speaker in a
too large room and have to supply too much power to it, it will
distort. True? It just can't play that loudly."
That's true.
"
So simply adding the subwoofer would not relieve the "strain" on the
drivers, it would only provide more bass, but I would still have to live
with the distortion, both from the woofer and from the tweeter (I'm
talking about a two-way speaker)."
True again.
"
If I did relieve the speaker of much of the bass load with a high pass
filter, you are saying that you believe in most cases the part of the
signal that goes to the main speaker would still be distorted?
"
It depends. There's several variables at play. If your amp wasn't straining to begin with, then you should still hear the distortion. A speaker can only play so loud. If removing some of the bass frequencies helps an amp that's being driven too hard, then you may be able to squeeze more volume out of the system.
That said, this is usually not an issue for your typical high end system. Most audiophiles are far more concerned with sound quality than volume. When an audiophile is looking for volume, it usually means something's wrong. When a system is sounding good, most people don't feel the need for loud music.
Your original theory, for the most part, is correct. Removing the low frequencies should allow a speaker to play louder, but its usually not a tactic used in high end systems. It's done all the time in car systems and pro installs like a night club.