REW without avr/pre-pro?

MIke, in order to use the EQ you have effectively you will need a calibrated mic and computer program. Then you can adjust things intelligently. You get your curves as flat and equal as you can and listen to that for several weeks. Then add or subtract a few dB here or there to get what you want. If the C52 has a USB input you hook your computer directly to that.

In order to get the best out of your subwoofers you need a full fledged two way crossover. JL Audio makes one but there are much less expensive ones out there. This will put a high pass filter on your main speakers lowering distortion and increasing headroom. This will make an improvement you will definitely notice. 

You only need an AVR if your system does theater work and you need the appropriate codecs. 

REW will work on your setup.  An AVR isn't needed.  you just need an analog audio input on the Preamp to connect your laptop/ Soundcard to and you'll be good to go.
You'll be restricted in your tuning tools, however, to tone controls, speaker placement in room, seating position and subwoofer placement/ subwoofer setting controls, only.  Which, in reality, is probably all you'll need.  I've had great results with REW in 2-channel systems by using just speaker placement and proper subwoofer integration.