I've always managed to keep these speakers working by using an older .kext, until Lion. The odd thing is that after installing Lion it worked at first, but stopped at a certain point in time, and fiddling the kext now is to no avail.
I've delved deeper into this now. Actually, the device works absolutely fine. The amplifier box contains a DSP chip that takes care of converting the digital data stream to analog sound and drives the headphone output, and a digital T-amp chip that drives the speakers with the signal provided by the DSP chip. You will find that the headphone still works fine under Lion. That means the basic sound conversion still works. What does not work any more simply is the switching "on" of the T-amp chip.
See here what I did to my speakers when I did not yet realise this:
http://www.cubeowner.com/forums/index.php?showtopic=13516
Basically I planned to use the T-amp as a standalone amplifier, using the headphone out of my mac mini as the audio source. I got that to work relatively okay. With an older mac mini it works fine, but with my last-year mac mini I get a terrible whine, probably due to some ground loop. Only in the process I realised that the device basically is fine, it just needs the internal amplifier switched on, which does not work any more on modern OS X.
You can force the T-amp "on" by grounding two pins on the board (pin 11 and 16, MUTE and SLEEP), which is what I'll try when I find a new/second hand set of speakers.