Plinius 9100 and 9200?

For that matter, what about the 8100, 8200, and 8200 mkII? Are these all just successive versions with steady improvements? Are the differences substantial?

Thanks for the responses. So is it safe to say that from the 8100 to the 9200 this is essentially the same amp with incremental improvements in each one but no earth-shattering improvements from model to model?

Thanks, now I understand. I think I should be looking in the B range.