By "plug that goes into the sub" I assume you mean the d-sub. It has screws on it. You screw it in. How does it come loose? Unless you're meaning the cabling for the satellites, which is a source of confusion for me, as I keep seeing some pictures that show them using RCA connections, and others that show them using more traditional speaker wires with clamp connections. Regardless, I'm not following you at all. If it's something that sits still all the time (with the exception of small vibrations) how is it going to come loose?
I've had my Z-640's going on four or five years now, I've never had any issues with them. Ever. Nothing has died, there haven't been any shorts, no cables magically come loose, no speakers have blown, no problems with the audio. I'd venture to say they sound just as good as the day I unboxed them, but since I can't really compare them to that... The only thing wrong with them, is me. They're four years old, I'm ready for something new. I'd also like to actually be able to connect my 360 to them and get REAL 5.1, and not just stereo coming out of every speaker. This is why I want the Z-5500's. They have the standard PC input, as well as Optical and Coax inputs. The 360 has an Optical out, couple bucks more on a cable for that, and I have true surround sound. It's been a long time since I seriously looked at the Klipsch 5.1s (I used to lust after those) but a quick check told me that while there's a good possibility they're superior and better constructed, they don't have Optical or Coax inputs. They're also 150 bucks more than the Z-5500's assuming you can find someone that sells them (I'm not a big fan of ebay).
So really, I guess, explain yourself more.
I've had two Logitech keyboards, three Logitech mice, a Logitech joystick, and the Z-640's. None of them have ever had any problems. Why should I expect otherwise?
[edit]
Just noticed you said 2.1's with another set of speakers. I doubt those have the inputs I want either, and then that's just quadrophonic, not 5.1. Of course, having not looked at the sub on those, I can very well be talking out of my ***, and it's entirely possible to add a center channel as well.
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