Jenn,

I understand his feelings and why he wants to do this. Being a caregiver thru all this I think you get his basic reason for watning to do this. The feling of being so powerless over the situation and having no control over it. Now that he's done and starting to have more energy he just wants to hit something tear up whatever this was that made him feel so poweless and not in control.
I too am no psycologist but I think that he is communcating with you and that's good. He's trying to express what's going on with him and not bottling it up like so many others might do.
I would just continue to communicate and maybe try to get him to compromise. I would be totally freaked out if my husband wanted to start cage fighting as well and my first thought would also be, " Your crazy"! It is not his charecter either to want to do something like that.
There are many avenues out there that your husband could pursue that are less physically damaging to him but would also give him the opportunity to vent. Maybe you could compromise with training in Akido or Taekwondo. they both have events of sparing and "fighting" but also have good philosophies that they teach in conjuction with the fighting technique. Tell him your freaked about this and ask if there is something else he can do that you both are comfortable with him doing.
I'm confident this too will pass. Mostly because I can see the two of you are sharing with eachother and that is the most important part of getting over this. being able to voice what is in your heart and mind is a bigger obsatcle to overcome then the physical pain and suffering of recovery. Hang in there Lady this too will pass.
~Ija~