I have 170's running with a 12" sub and the combination sounds excellent.
I used the same sub with a pair of Vandersteen 1B's and a pair of B&W 602's.
The mids are cleaner than either of those models, and the highs are less fatigueing and more detailed as well.
The only penalty incurred with smaller speakers would be in dynamic capability, or the difference in sound pressure levels from the softest sounds to the loudest. A larger speaker will be able to play louder in side by side listening. That does not mean the sound QUALITY will be better because it plays louder.
The 170's have been so good for music, they have inspired me to upgrade my sub to bring the low frequency detail up a notch or two!
Ed
* Sierra-2EX's W/V2 crossover upgrade
* (2) Rythmik F12's
* Parasound Halo P6
* Audio by Van Alstine DVA-M225 Monoblock Amps
* MiniDSP 2x4HD For Sub calibration
*World's Best Cables Canare 4S11 speaker cables