Thanks for the suggestions. I tried them all, but the problem continues. I disconnected all USB devices from the computer except the GX and the keyboard. I unistalled the old driver and reinstalled the newer beta driver. The system still had very reduced bolume and I was getting USB device overpower warnings.

I disconnected the GX after my original post, and the system worked fine. When I re-connected the GX today, both before and after the software install, sound output was reduced to almost nothing. I also double-checked my Bose external amp and speaker system by running it direct from my iPod, and it had normal volume. When I disconnected the GX and ran sound output directly from the compouter's internal audio to the Bose system, volume was back to normal.

Checking the system profiler data, it appears that the GX nominally draws 498 ma while the bus supports 500 ma. Seems conceivable to me that the GX is experiencing some sort of internal glitch that is limiting audio output and creating occasional surges in currect draw that overtax the bus. The keyboard only draws 20 ma.

Based on all these tests. I'm now more convinced than ever that this is a hardware problem with the GX. I'm also sure it's not a Snow Leopard/Driver conflict because the system has worked fine for several months with Snow Leopard.

I would like to get the GX repaired or replaced. What is the procedure?

Once again, I appreciate your suggestions, and I tried them all to no avail. Output sound volume is still restricted and the GX tends to get kicked off the USB bus for drawing too much power.

Just to confirm:

I have always run the GX at max output volume and controlled listening volume with the Bose volume control.

The input cable to the Bose works fine from the computer but doesn't work from the GX except at greatly reduced volume (With the GX in the circuit, I have to turn the Bose to max volume to even get the sound to a low listening colume. Before these troubles started, I could pretty much knock plaster off the walls with the Bose volume - either through the GX or straight from the computer - there was no discernable difference.)

I installed the new Line 6 Monkey and ran it to update my LIne 6 software. I re-started after installation and ran the Monkey again to confirm everything was up to date.

I have watched your videos and read all your online Mac advice about sound issues more than once, and it appears that I am following all your recommendations to the letter.

I have been using the GX as my primary input and output interface since October with no problems until recently, when all the trouble started. I did not make any software or hardware changes to my computer system.

With your guidance, I have taken steps to rule out every conceivable software or setup issue and the problem is not solved. THE BOTTOM LINE IS THAT THE GX IS NO LONGER WORKING PROPERLY AND I NEED TO GET IT REPAIRED OR REPLACED. WHAT IS THE PROCEDURE TO GET THAT ACCOMPLISHED?

Here's an image of my screen. The GX once again shut down with this warning.

Also, I am now unable to get any signal into the computer through the GX.Wait! There was just a loud POP and the sound tarted coming in from the guitar - nice and loud like it used to be, Wait again. Nnow there is a USB overpower warning and the GX has been disconnected from the bus and the pilot light on top is dark. This is my life with the GX !   Let's get this dfamned thing repaired!!!!