Sorry. I'll take that back. I can neither find anything at the avid site about it. I see what you mean. I think I remember that I read something about thirdparty hardware at the avid site for some months ago, without can be 100% sure.
"http://www.mackie.com/products/
onyx1640i/"
"• Qualified by Mackie for use with all major DAWs, including:
» Pro Tools® M-Powered™ 8 (Requires FREE driver upgrade download)"
-from the Mackie site.
There is also a link therefrom;
http://www.mackie.com/products/onyxiseries/drivers/
In this site is a link to driver update for a Onyx mixer(from Mackie) To be a compatible interface with M-powered. Think I have seen other brands as well have the same thing. The new Avid site is a mess, after my opinion.. Really thought it did stand something clear about it there..