A couple of years ago, I had almost the exact situation as the OP - sound problems with the IFE in my seat in F.
Crew tried to reset my system, brought me different headphones = nothing worked.
The CSD immediately offered me 10,000 Avios and said that was the maximum they could offer. I accepted, and that was the end of the matter as far as I was concerned.
The crew were apologetic and also offered me a bottle of champagne to take away, which I didn't accept as I'm not a champagne fan and didn't want to carry it on my onward journey, but I appreciated the gesture.
The experience did teach me to load my iPad up with entertainment before a flight, just in case the IFE does fail again.