I would think 8 ohm is the default as well. When you run Audyssey, follow instructions to the letter, use all 8 positions, and don't be shy to sit the mic up high enough (2-3 inches) to well clear the top of any high bench of your couch, and point to the ceiling. In addition to setting up the distance, levels, crossovers, XT32 Sub EQ HT can do some other good if run properly.