I don't think you'll void the warranty. As for DIY "repair", as you've found, you won't be repairing it. But, the removal process and re-installation is pretty simple. The hardest part is getting the amp to come free of the gaskets, which just requires a little elbow grease (and, maybe, if you can't get a good handle on it, a nice plastic pry-bar used to remove interior trim pieces from cars).
None of those are what I'd consider "big".
Deep See Sound is one guy (@dgage), AFAIK
. He may have expanded, though. But, even if it is one guy, it's one guy who provides, from what I hear, exceptional support and is very excited about audio -- even driving out to customer's houses to help set things up. But, that's what it takes when you start out to make a great name for yourself. And, as you get bigger, that kind of service gets harder to maintain. Of course, I wish him all the luck, and am considering supporting his venture myself. I've met him at a local get-together years ago. I remember he bought some JTR speakers and was...harangued...for talking ***** about their lack of bass / mid-bass. I find it quite awesome that he's taken that passion and built a sub-woofer company to create products to provide crushing bass while being capable of producing pretty clean mid-bass as well.
JTR also has a commercial side of the house which may help them. But, I still think it's a small shop. Maybe not one-man like Seaton, but not large.
I don't know much about Rythmik, but I don't think they are really big either.
Thus, if you're worried about a company going out of business and no longer being able to support you, I don't think any of these shops are as...financially stable...as, say, a JBL is. But, if you limit yourself to larger, more corporate, offerings then you'll both pay more and get less. So...that's the risk you take. And, guess what, JBL could go out of business just the same, it's just less likely.