Did a few edits - used the strikethrough feature to help show what i changed
RCA is two mono cables, while 3.5mm TRS is one stereo cable.
Both carry a 2.0 sound only, the subwoofer filters lower frequencies off to itself based on that knobs setting.
Hi just a update.
Overall very happy with these speakers and are very easy to recommend with a caveat.
I've connect the supplied 3.5mm cable to the headphones jack of my HDTV, and given my HDTV is connected to my pc via hdmi, I can leave it like that and watch pc content and use my bluray player.
I paid $220AUD for these, and they're 200w total, however the next cheaper set of logitech 2.1 has only a crappy 60w total, so I'd avoid them like the plague.
One problem with dvd/bluray playback is that when you run a 2.1 system, you have to goto the player settings and change Dolby digital and DTS from bitstream to PCM stereo otherwise no sound.
So I popped in Terminator 1984 bluray into my player and the sound was impressive on bass, laser shooting and the scene in "Tech Noir" where Arnie uses a machine gun, but some of the dialogue is a bit quiet and nothing can be done about it using the bluray player.
So if you plan to watch movies on a stand alone bluray player, you'd be much better served by the 5.1 z906 that can decode both Dolby digital 5.1 and DTS 5.1, however on pc, you can use your VLC player to increase sound beyond 100%, so on pc these are worth every cent.
I had to learn most of this over the last few weeks.