bori, I have my X-over set at 80 Hz with all my speakers set to "small". I have the Primus 360's, PC350, and the 150's in the rear. Thus, the 360's can play a bit lower than 80 Hz but I have found they sound better when left at 80 Hz. I have tried them set to "large" but notice no real advantage. In fact, it kinda muddies things up a bit due to some over lapping between the natural roll-off of the 360's and the 3.3 X-overed set at 80 Hz. I suppose this may be due to some cancellation/phasing issue(s). The best thing to do is to experiement around with the "small" and "large" settings as well as different X-over points. Only you can really decide what sounds right to you. My receiver allows for X-over settings of 100 Hz, 80 Hz, or 50 hz. Of these, imho the 80 Hz X-over point sounds the best in MY room. Once again it may be a good idea to consult w/Dr. Hsu or Peter Marcks as they both are more knowledgeable than I. Hope this helps bori. Craigsub may can offer some sound advice as well.