I'm currently saving for a nice set of surround speakers to go with my fronts (Energy Audissey A3+2) but in the mean time, thought about using a set of older Bose speakers until then. The question that I hope someone could assist with is the issue of speaker impedance. The fronts are rated at 6 ohms but the bose are 4 ohms. I'm not sure how safe it is to mix the two sets? Any thoughts on if it's safe and if it isn't suggested, is there an effective way to raise the impedence on the bose? Thanks.