Don't know you're musical tastes, room size, or what things you listen for. Single driver speakers provide a direct connection to the amp (they are "active" speakers by definition). They typically are easy to drive (and efficient, the advantages of high efficiency drivers cannot be understated.) Single driver speakers have no crossover distortion, no phasing issues between drivers, cheaper to build with resources going into the quality of driver. With multiple drivers you hear two or more sources for the same sound (especially nearfield). With woofer/tweeter arrangements you also hear two different sizes/types of drivers trying to reproduce the same signal at crossover frequencies. What extended range drivers do best is the heart of music, the 6 octaves from 80 - 5000 Hz. Much heartburn comes from trying to stretch into the last two octaves that marketing types tell you are so important.

Single drivers have limitations: deep bass, narrow dispersion of higher frequencies (beaming), and lack of ultimate sound pressure levels. The Martin King/Bob Brines offerings pretty well address deep bass for nearly any musical type. Beaming can be made into an advantage to tune to a listening position and reduce first reflections (improve imaging). Until you've played around with a sound pressure level (spl) meter most overestimate how loud they listen, so they think spl is an issue, but in reality it's rarely a problem unless you're a young headbanger that'll soon suffer permanent hearing loss.

Another easy/cheap avenue not mentioned so far is single driver open baffles. That's right, just take a sheet of plywood/whatever and mount a extended range driver in it. The bigger the sheet the deeper the bass. Dynamics are improved, imaging is life like. Open baffles work best with drivers that have a Qts of say 0.6 or higher. The Visaton B200 (about $150 each) has been a very popular candidate lately for high efficiency open baffles. Like most single driver speakers you may want to add a sub. Again, the Bob Brines speakers are about the only exception to this rule. See Bob's forum elsewhere here.

Another place to check out is Decware. Steve Deckert lives fairly close to you in Peoria, IL. Decware offers high efficiency speakers, tube amps, cabling, even some player mods. It's a small shop that builds quality stuff for a good price and offers personal attention.