I have USB Loader GX and Configurable USB Loader together on mine... I noticed when I had USB Loader GX by itself, it didn't play song clips. Now, since I also have CFG USB Loader installed, they both play sound clips. I guess it was just a folder that was needed. GX still doesn't show the back of the games though. I'd actually recommend CFG instead of Wiiflow... I think the various themes, especially the Matrix theme, look better than anything on Wiiflow. Just my opinion though.
I guess I didn't really answer your question but it was semi-relevant I guess.