I've used an SVS SB-12NSD for about 4 years, both with standmount monitors and with big speakers. Avoid the high-pass in the sub, as it will likely affect the transparency of your signal to the bookshelves. Send full-range signal to the bookshelves, and start by crossing in the sub pretty low, trying 45 Hz at first and then 60 Hz to see if things get too wooly. If you can locate the sub in space with your eyes closed, then you have its level or crossover too high.
Have fun!
Have fun!