Yesterday I purchased another Klegg MediaShare from Fry's in hopes that they had improved codec support (it was also an 'open box buy' for $85) in the several months since I last tried one out- but it looks like they have been pretty stagnant with overall support. It appears that device has been re-branded under several names (such as the Novatron IAMM NTD36HD and the Zio eUreka LX350HD) with compatible firmwares, but none of these vendors are offering the one codec feature I am looking for: mkv file support.
I returned the Klegg MediaShare to Fry's earlier today.
While doing research for the Klegg firmware, I ended up at the Wikipedia entry for HD Media Players and at the end of the article they mentioned the Popcorn Hour player (cheesy name, but it sounded promising when they mentioned it in a HT Guys podcast). I found a good review (and video review) and it looks like almost everything I am looking for (plus some additional features such as YouTube, Flickr, and RSS feeds!).
I placed a pre-order today and hopefully i will be in the August 11th batch of shipments...