Current setup:

Sony STR-DE835 5.1 receiver - 100W per channel
Polk RC85I in-wall surround speakers (5) – 8 ohms 100W per channel
JBL HTI88 in-wall passive subwoofer – 250W max
Onkyo M-282 2 channel amp 100W per channel at 8 ohms, 125W at 6 ohms

I have the Onkyo amp connected to the JBL sub. The sub has 2 8" woofers, and my Sony receiver has 2 sub outputs. So should I set it up as mono or stereo? I have the JBL installed vertically on the wall, so the Right would be on top and Left on bottom if stereo is used. Is there really a noticeable difference?