Honestly, I doubt the Mirages will sound much better after the "break in". I think your biggest mistake, as you said, was "mistake number 1", which was listening to a lot of people's opinions and "reviews".
No doubt people online are trying to be helpful, but more likely than most, people are just going to recommend what they own and trying to hype up to themselves that they made a good purchase. Simple as that.
While it's good to read other people's opinions, they should really only be used for learning about different speakers for you to check them out. You always need to demo any pair yourself before considering buying them.
As with your case now, you can wait and see if the Mirages improve any over time, but definitely demo the new ones if you are going to make a switch.
With regards to the B&Ws, the CM line is generally more "detailed" and slightly "bright", in my opinion, while the 68X line is "warmer" and more "muscular". The CM line with a good sub is probably "better" for my tastes, but they are also more expensive. The 68X line packs more value, but with the 683s, you are going to have issues with the matching HTM61 center, unless you can use another 683.
If you liked the 602 s2, you might as well consider the 685s instead. Then you won't have to deal with the off-axis dispersion of problems of the HTM61 as the matching center for the 685s is the HTM62 which is fine.
If you're staying with the "phantom center" though, then it's not even an issue. Best, however, is to listen to all these speakers first and buy what you like best at the price you want to pay.