@Antedeluvian: Did you buy Joseph a pair of suppressors as well, or does his taste lean towards his mother's?
I don't know if it's just the younger generation, but Joseph seems quite happy with his earbuds in his ears -- he's impervious to anything that's going on around him -- plus in the car he tends to go into hybernation and sleep most of the journey -- he's great to have as a travelling companion because you rarely even notice he's there.
May I suggest a low tech solution? Those little spungy things that you roll between your fingers before inserting into the ear canal work quite well - and the are really cheap.
I once escorted my son to a rock concert. The bass was so loud that I could literally feel it move my shirt against my chest. The high end was painful. Those little spungy things worked wonderfully to remove all pain and I was not an embarassment to my son. Can you imagine walking into a rock concert with those flight-line ear muffs? Sorry, I love my son too much to do that to him.
The little spungy things don't help much with the bass, but I suspect that those huge beasts you love don't either.