The Contact info for the domain appears to be that of their webhosting company. Have you called them?...most hosting places won't give out details of their customers, but occasionally one gets lucky and can garner some useful info.
Old copies of the site on Archive.org weren't much help - no address, no phone number, no email, etc.
However, based on what I've seen there along with the history of their trademark registration (lots of problems), my hunch is there's a very good chance the "Attorney of Record" who filed the registration is also the domain name holder - may be a direction worth pursuing in finding the registrant.
My suggestion is to tread softly and don't mention anything about trademarks, etc given your mark isn't strong either at this point ... instead focus on buying the domain - it's obvious the registrant of the domain could never make it work and basically abandoned it, so it's very likely they'd be agreeable to sale for some quick cash.
Lastly, domain name recovery/acquisition is as much an art, as a science so definitely ask around for opinions on approaches that may work.
Ron