I'm going to be honest right out the bat and say I'm not totally sure how this would be done (esp while maintaining enough to still let the player know they're being hit).
All players have the option to reduce sounds in the game right? It can help for a lot of reasons, esp. for players that get really over stimulated by the loud sounds but still need to be able to hear people talk and sometimes still be able to hear around them a bit. I tend to avoid pvps because the visuals can also get kind of intense, especially when people flick grenades and it scares the living sh-- out of me w/out warning. Like I said, I know this would be difficult but it's putting me at a disadvantage with the dailies (which I mentioned another issue I have with those in a different post) because so many of them are pvps and constantly require players to play (kind of a lot of) laser tag and paintball without much variation.