Welcome to the saloon, Huskerwing.

I did a quick search on the Epos ELS-3, and the -3dB point looks to be around 65Hz. With that in mind, I'd tend to recommend using the RR2150's built-in bass management (setting it to 80Hz), either bypass the B&W's crossover or set it as high as possible (so it doesn't interfere with the RR2150's crossover), and take a little time with a calibration disc to get the sub's trim dialed in relative to the speakers. You may already have a disc like Digital Video Essentials (which has a test tone in it somewhere that will do a sweep from 20Hz on up, so you can use an SPL meter to tweak the sub level relative to the speakers), but if all else fails there's also my Devious Tiny Disc (see "Gonk's DTD" in my sig) - it's not really a calibration tool, but it will give you a frequency response sweep that could be used for this task.