I have a Harmon Karden receiver right now and I have just two tower speakers (I think there are three or four speakers in each tower). I'm running the receiver in STEREO mode right now. Eventually I'm getting a newer receiver that has HDMI as mine just has component and I want a quality set of 5.1 speakers but I was thinking about buying the powered subwoofer first. Can I run the sub now with the tower speakers instead of 4 surrounds and a center channel? Do I continue to use STEREO mode or do I have to use another mode in order for the self-amplified subwoofer to work?