Hi fredk,
In the case of the old M80ti and the M80 v2, quite a bit. I sent a PM to willscary but it isn't as if it's a big secret. In the summer of 2003, we (myself and Axiom colleagues) did extensive double-blind listening tests to the crossover-tweaked M80 v2 and the earlier M80ti. The new v2 version won the tests and I was very pleased. The tweaked version has audibly smoother upper midrange response that's noticeable on vocals and especially brass and reed instruments and strings.
The crossover change was a running one in the summer/fall of 2003, but the model number didn't change until late 2005.
Regards,
