Less is more? Where's the midrange question -help

I've been furiously wondering about this for years -
Be kind, I'm just now making the move to serious audio!

In short:
Why is it that when you move past Polk, Mirage, Klipsh, whatever upper low end, and move onto mid high end you lose the implied technology and number of drivers? Most of the lower end stuff at Tweeter or Circuit City (sorry) have a tweeter (or horn), a midrange or two, and a woofer. Moving up the scale and dollars results in speakers with only 2 drivers.... How do you get accurate midrange from a 4" or 6" driver?

To be more specific -
I have recently purchased a pair of Audio Physics Tempo III's. I have yet to find the sweet spot. They sound muddled and harsh. I have a Yamaha amp, but will be upgrading shortly to an Aragon 8008 ST.
I am listening in a somewhat small room, plan on moving the equipment into the basement shortly.

Here's the reason for the question and thanks for reading this far down!

I have two (be kind) Radio Shack Super Tweeters that I think sound incredible. They were $20.00 each 10 years ago. They seem to bring definition when hooked up in parallel with my Tempo III's... more to the point, I have Klipsch satellite speakers (in plastic boxes about 6" high) which bring out the midrange and clarity of strung instruments when hooked up in parallel or simply playing as "B" speakers while the "A" speakers (Tempo III's) are playing.

How do you get the midrange with out a driver tailored for that frequency? Do my $3,400 Audio Physics Tempo III's have a midrange deficit?

Any revelations for ideas greatly appreciated!!!