It's actually very confusing what is a version one, and version two. and the like....
The version one/or very early remote had no surround buttons.. so I think that's V1, and the V2 has the buttons on the top to control extra mainframes.
At some point.. around version software 4, the V2 mainframe came about. The differences.. a better converter..and changing the rear metalwork, adding an Optical input.
But as Alan has pointed out, they just made a plugin card format, for user upgrades.
Have a late V1 mainframe with the V2 surround ready controller, and use a small box to covert my optical to AES (just for the computer desktop/itunes) Must say, the converter is great! heheh
Over all, the manuals are very badly written, and it's taken a while to navigate all the hidden stuff... but it's all good!