Does it work with other loaders?
If it doesn't work with other loaders, it could be because of the used cIOS.
1. Connect the Mic before launching the game (or before launching the USBLoader?)
2. Try another IOS Base. Your cIOS on slot249 should be Base56, try to launch the game with IOS250 (should be base IOS57). Some music game may require that you use a base IOS58 (if you don't have it, you will have to install it using modmii or d2x installer. You can select the slot you want to install it, IOS248 is a good idea. Maybe you already have the base58 installed in one of the slot 240 to 248)
3. try to update your cIOS (there are v10 of d2x, and two different version : normal and alternative)