I have not heard the mkII but I think the evolutionary description is probably accurate.
When I inquired on this topic a while back when I was looking, John Strohbeen told me that the difference is the new soft dome tweeter used in the Micro Walshes and Series 3. I recall he said the actual Walsh drivers were the same.
Now there are some even newer versions of the larger drivers alluded to on the OHM site over the last few months, like 3000's I think,that are also designated evolutionary soundwise and use a newer version of the Walsh driver with higher sensitivity, better magnets, etc.
Two things I must say about John Strohbeen from the few times I have talked to him, the information he publishes on the web site, and my experience with his products.
- he has a very modest, understated and unpretentious way of saying things
- what he says seems to almost always be accurate nonetheless
