They are just 3.5mm jack. However, the system has worked fine - for a time. When the plug is put in, the socket symbol on the right, blinks (used to blink) just as Bush mentioned.
Indeed, when I followed Bush's instructions on loading the sound menu system, it worked for several days, leading me to believe that it had solved the problem. Then it just stopped - with no other device having been plugged in.
If it were just a case of buying more modern speakers, I'd go with that, but I'm still uncertain what's causing the intermittancy.
Oh, one thing. When the Windows Volume control is raised, one can see the green bar bobbing up and down when music is playing.