this link will take u to a comparison chart at access.
http://www.access-music.de/comparisonchart.php4
this chart compares specs of all the virus models. im not sure if the chart contains the current changes to the C series OS though. (the new extra filter)..
when u ask upgrading to the latest OS. do u mean upgrading to the latest OS for each model? u can only upgrade the OS for the particular model A,B or C....the latest OS is only for the C series, not the older models..
hope this helps ya out a little..