well, guessing from your original post you seem to know the sound of the Minimoog, which is (usually) a single voice...
your box should sound at least 'reasonable', even with it's original firmware
if it sounds crappy and does a lot of strange things there may be more than just the firmware not working - which is only a guess (I've not heard your box, nor do I have any idea what's precisely inside...)
the number of voices may indeed be related to firmware - I (vaguely) remember the original version was delivered with 6 voices and they later changed it to 12 (maybe it was a conservative guess, maybe different chips or programming...)
noone can tell from hearsay if your box is ok or not, fixable by firmware update or not - but it's supposed to sound like a real Minimoog, not just a little bit 'moogish'

There are more than enough soundexamples on the net that prove this.
cheers, Tom