Have you tried selling this to hi5.com? Also - TM is not an issue depending on its uses. Since the term "hi5" is soooo common, it has many uses and a company (in this case hi5.com) can only trademark for certain genres.
I think you have a great domain at least in the $X,XXX's depending on who you sell it to... Everyone gets so into the fact that it is a LLN.net and they don't realize that "Hi Five!" is one of the most used phrases in the english language.
I definetely recommend trying to sell this to hi5.com.