Ya know every time I have ever had Bison it was tuff, and its always served rare. Bison like Elk and Moose are really red meats.
I have never cooked Bison, but if it was me I might try a brine. But don't take it as a suggestion because I don't know. You might cook the ribs like steak, let them absorb some smoke than toss on the grill. But again its just guessing on my part because they should be like lean beef ribs.
BTW we are all here to help and someone knowledgeable will know, but in the mean time might I suggest you drop by the forums "Role Call" section so you can get a proper introduction for the masses. You do want to get the secret handshake and password anyway don't ya?
You might also click on the above toolbar, "My Profile" and tell us quickly about yourself, as specific or vague as you can stand. Most important though is where ya hang your hat at night. It will help us and you understand questions and answers in a discussion or help understand why you would says something. I could tell you about a real nice crawfish pontchartrain sauce for those ribs and you'd wonder why I said that. LOL... its easy fast and we'd sure appreciate it.