OK, here's the deal. I was using a pair of Logitect X140 speakers (2.0 - powered) that were pretty good, but the bass was lacking. In town this week WHSmith had the X-210 speakers (2:1) for £19.99, so I bought them and hooked them up. Now this is a limited system, with no independent control of the sub, but the bass was much better. Unfortunately, the satellites have a tendency to distort at higher volume levels. Anyhoo, tonight I hit on an idea, which is to dump the satellites and plug the X140s into the X210 sub.
The sound is now exceptional, but can anyone confirm whether or not I'm likely to blow anything up in this configuration. As I see it probably not, since the only return from the X140s to the sub is ground, but a second opinion would be nice.
The advantage now is that I can set up the balance between the front speakers and the sub separately, and I have to say, listening to Jeff Wayne's War of the Worlds is a pleasure :)
If it works when you first try it, I see no reason why it should blow up. :)