What is the difference between McIntosh MC275


I am thinking of purchasing a McIntosh MC275 amp to power my Tannoy Turnberry GRs. I can get a pretty decent deal on a new MC275 VI but I can also save a few thousand by purchasing a used unit. Can anyone tell me the differences in the IV, V and VI versions of the MC275 and if there are are differences sonically between the units.
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There is this thread:

http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1384657026&read&keyw&zzmc275

And I feel like there was another on this exact topic very recently but couldn't find the thread. Do some searching though the info is here.
That's perfect. Thanks Jond - much appreciated.