ok you really need to disable the 'internal' amp on that radio. You should only need to clip or disconnect one wire, iirc there is a thin wire running from the main board to the amp board, that is the one you need to mess with. you could also put that on a switch so you could run the radio barefoot or balls out. That radio SHOULD have a pair of IRF520 finals which would give you between 25 and 50 watts out on their own. That would be perfect for driving your texas star
BUT if you keep running the radio like that your Texas Star is going to die, there is NO way around it.
I did this same modification for a guy with a Galaxy Saturn Turbo, but for a different reason. He did not want to run the Saturn's amp if he did not need it.
if you can get some good pictures of the inside I could tell you how to do the modification for sure (for that matter I would do the mod for you for free if you are a local)