I sort of expected a generic USB speaker driver to install. Is this too optimistic?
If you mean on the Logitech installation disk, yes. Not likely to have Linux drivers there.
If they are connected by usb port, run "lsusb" command without quotes and post the output, particularly anything pertaining to speakers.
You could try search by the name of your speakers and add Linux to it on google or whichever search engine you use. Have you checked settings in KMix, should be a sound icon or you could run alsamixer in a terminal (as root).