I'd like to suggest that you think long and hard about what exactly you really want out of this, and how you are being harmed. If you feel you are being financially harmed, and you want to be paid for your work, then have your attorney send him a letter demanding payment for use of your work. If you are not looking for money, then you're only looking for essentially an ego boost because you want some sort of public acknowledgement of your work. I would suggest that even if you get that, it is not going to amount to anything. You should already know in your mind what you have done and what you are capable of. Do you want to merely be able to promote yourself? Do you have recordings of the same material so that you can use them for auditions and such to show people samples of your work? If so, then you are not really being harmed by this, as I see it. The only thing being harmed is your ego. But what is stopping you from creating a web page and posting all of the same music and saying in big bold letters that it was you that engineered and played and wrote all of the tunes? Wouldn't that accomplish what you are looking for? Or does his website have such high traffic volume that there is no way you could get people to notice your site because they are all flocking to his?
This issue resonates with me because I suspect that one reason many of us got into playing music in the beginning is to get some sort of fame and recognition. At least back when I started in the 70s, that was probably my goal, subconscious or otherwise. I wanted to be on stage in the limelight and have all the girls swooning in wanting to meet me backstage. It was not about the music, it was about the recognition. The wisdom that comes with age has taught me that feeding the ego is a fruitless exercise. No matter how much you feed the ego, the ego is always starving for more. In reality, there is just no point in doing that. Much better is to just enjoy the creative process and be satisfied in your own mind with the fruits of your creativity and labor, without requiring any sort of external validation. You can be much happier that way. And actually, happiness is really what it is all about. The goal of life is to have fun and be happy. If you are going to let someone rob you of your happiness by getting all bent out of shape over something inconsequential like this, that is just a shame.
Another thing to think about: If hypothetically your attorney sent him a cease-and-desist letter saying that he needed to either remove the material or give you credit, and he did one of those two things, would you truly feel better about yourself after that happened? What would change for the better in your life as a result of that action being taken? It strikes me that you would feel like you won and he lost, and that would be the ego-boost that you are looking for. So again I suggest that feeding the ego doesn't actually work.