Foremost, I am with you, I wish I set mine up a year ago too.
So, I will relay what I have been told from Harman and Kardon and Microsoft, but take all of this with a grain of salt.
Harman and Kardon said that updates cannot be done manually, and that all updates are processed over the air. I ask them about the servers, to which they said that if Microsoft pulled the servers, the Invokes would not work all together. Microsoft told me that all Firmware updates for the Invoke, are processed by and or at Harman and Kardon, Microsoft does not have access to the Firmware servers. Basically, Microsoft said it is not their problem, Harman and Kardon seem to be blaming our networks, than our devices, in that order. Since most of our Invokes are out of warranty, Harman and Kardon recommended that in my case, I take them to a repair center.
In navigating this issue, I cannot help but feel that both could be at fault. With all the changes coming to Cortana, it is highly likely that Microsoft broke something in the coding, or simply changed it, so less end users are supported. I saw this happen first hand with Windows Phones. Likewise, since Harman and Kardon have completely erased the Invokes existence on its website, them shutting things down seems quite probable. Whoever is at fault, I feel confident in saying that I do not believe either one anticipated the end around many of us have found, to get this thing to at least somewhat work. My bet is that will be "fixed" sooner rather than later.
Cheers,