Best Used Speaker Under $4,000 w/ Respectable Lows

I was once a member of the audiophile community (Some of the older Audiogon members may remember me) but had to step out for a bit do to life changes. I am thinking about stepping back into it in a limited fashion with the system configuration listed below. I would love opinions on what used, $4000 or less, speaker would best suit the following system. Note that I would prefer NOT to bi-wire and would love something with a respectable low end (A full range speaker would be nice). I tend to treasure transparency, neutrality, high end extension, speed, DYNAMICS, and tight driver control / integration in my speakers and leave bloom/coloring/musicality to the amp. I also prefer speakers that play very well at low volumes with medium power amps. Thanks for the help!

Transport: PC with Windows 7 / WAV Files / Foobar / Lynx AES16 PCI digital I/O card

Dac & Preamp: Berkeley Audio Design Alpha DAC

Interconnects & Speaker Cable: Nordost SPM

Amp: Sim Audio Moon W 5.3