I have them plugged in to my TV via the headphone jack. Matrix mode is on but it's definitely not the same as true 5.1. To tell you the truth I haven't tried true 5.1 with these speakers yet - I want to use them with my computer but my computer just got bought and it hasn't shipped yet.
As for sound quality, it's what you'll get for the price. Not too good but definitely not bad. The bass could be louder. Again I haven't tried 5.1 yet.