Hmm... sorry, I'm a bit confused..

if I visit www.kmm6.com/Blog it redirects me fine to www.kmm6.com

If I click on a post, it loads the post fine as well.

You're using b2evo-v2.0.x if I'm not mistaken, right?

To set the blog (Blog A or whatever blog you want as default) do:
- in backoffice goto App settings -> General and select another blog in "Default blog to display".
- To disable the All Blog (blog 1) goto backoffice -> Blog settings -> Display -> "Display public blog list". If you untick this, the All blog (blog 1) will still exist, but will no longer be displayed in the bloglist (that is the row with tabs for each blog, most often seen at the top of the blog).

If you want more finetuning, I suggest you read the section on Stub files in the manual (This is the technical way, so if you get stuck, do ask again in the forum).

Good luck

*edited*