Usually, the USB port on a TV is for plugging in a pen drive or external HDD to view your photos on the TV screen, but your TV user manual should explain that in more detail. The TV USB port is not an output for TV sound, so what you're trying to do won't work as it cannot feed sound in to your HT. Doesn't your TV have a 3.5mm headphone socket? Or red & white RCA outputs?
As regards the USB port on your HT, it may not be an audio input anyway, so again it's not going to do what you want even if you use the correct output at the TV end -- you'll have to check the HT manual to find out what the USB is for.