The thing about the BM6as is that they have a great midrange and overall good balance, but they roll off way too high and their low-mid isn't very detailed. You see I made the mistake of getting sucked up into Gearslutz, trying out most of the shit they rant on about, and now I can actually see why any of the lower price bracket monitors won't cut it. I've tried just about everything in those brackets short of the Focal Twin 6 (which is sort of my last hope, even if it is butt fugly).
The O300s are not like listening to a speaker. They're like listening to the source. There's no real way to describe them to somebody who mayhaps hasn't heard speakers in that price/quality range before. It's one of those love at first sight moments where you just know if you get this thing it'll be paired to you for your whole working life.
It's this whole spiel I've been having internally about settling for cheap because the bands here don't warrant it, or following the dream and getting what's truly desired. It's a trade-off of simply having what one needs, or considering that one still wants to be the very best metal/rock mixing engineer in the country.
Your fave, Jens Bogren, mixes on a pair of Barefoot MM27s and those things are a few grand more than the O300s. Can you imagine the sort of detail and quality we're talking about when we get to mixes of that caliber? There is no way a set of 2-way speakers will cover all the ground for you.