PC speakers?

I have a Dell PC with iTunes that my son just started to use for playing music. The current speakers are Harmon Kardon with a sub. There is one wire that comes out of the sub to power the two samll cube desktop speakers (it splits into two wires) and one of the cubes does not work. What would be a better choice to work with the existing sub, not too large and can sound better then the cube speakers? One of the cube speakers has the volume and on/off control.

Thank you.
What is your question?

Are you looking for new speakers to work with your existing sub? Are you looking for a whole new system?

Usually small PC speaker systems with built-in controls on one speaker can't interchange easily with other products.
Steuspeed, would perfer satelites to work with the existing sub but I am open to additional suggestions.

Thank you
Well, I did a little looking around and these NHT M-00 speakers look pretty trick. These would be a step up from the typical plastic PC speaker set-up.

The NHT are powered monitors, I would like the monitors to work off the existing sub.

Any other suggestions? Thanks for helping.
Well if you have a sub, power and volume control capability I would suggest Gallo Micro speakers.

Steuspeed, thank you.