I recently purchased the Logitech z506 speaker set, and it sucks. I can't play opera loudly without the speakers crackling. Whenever a voice goes up high it cracks, and even loud orchestral passages. And there is a constant quiet cracking/hissing sound even when nothing is playing. They seem like cheap toys. I'm willing to pay up to around $300 or even $350. I know the z5500s are good, but they've just come out with the z906.. are those any better? Also, what kind of sound will I get from my Mac Pro if I just plug them in with a single 3.5mm cable? Do I not get actual 5.1? Thanks!