would it be possible to wire 2-channels from a head unit to one speaker, so that in essence the head unit would be "bridged." If so, is this smart, b/c i might drive two speakers like this from my head unit and use a 2-channel amp for my other more powerful components
Whoa, I wouldn't do that to your HU. Most manufacturers will not recommend it. You can also email the company of the HU for advice to double check. Have you thought of getting a 4 channel amp?
If you're not overly rich, MA Audio makes a 4 channel amp that's good for the money. Here's the model to try, HK597. It's got pleny of power in reserve for the future. If money is no object, then try Kicker/Rockford/JL/US AMP 4 channel models. I've already upgraded my system and trust me, it sounds 10x better than the HU.