Wrong forum (You want the NG forum for a TSU7500) but I do have questions for you. Bear with me because I've not had one of these remotes for over 9 years.
1. Did you use a PC to setup the 2nd Pre-Amp 'Device' or are you trying to do so on the remote itself?
2. Is this button that is grayed out on the 'Devices' page or on a page that is jumped to after pressing 'Preamp 2'? If the buttons are on this 2nd page, they won't be pressable until you assign a function to them or load an IR code into them.
3. Did you try to upload your config from the device to a PC? If you've done that, could you please email me the config to the address on my profile and I can take a look over the weekend.
