Hi Michael, for me this post hits the nuts of it....and that is, what's the easiest way to get it done right....
I gotta start by saying I'm totally sold on the driver-by-driver approach...
I understand that correcting driver by driver is a minimum phase effort.
But electrical x-overs filters aren't...(if i understand correctly).
I have experienced a huge amount of time consuming trial and error trying to find x-over filter types, orders, and points that gave the desired acoustic center.
Just for on-axis....move off and it's a whole new set of trial and error.
And IMHO, it's mostly due to sloped phase......
So for me, to get magnitude and phase flat driver-by-driver before I go to x-over, shortcuts all kind of time and effort....
If I can get mag and phase flat through, and maybe even past the critical region, simple symmetric LR works.....and then I can simply shift x-over freq for off-axis response, without any other redo.
And yes, I hear you re latency, and the temptation to over do mag and phase flattening too far out of band...(where it won't work anyway!)
I'm beginning tuning with all the taps I've got...
I can see from measurement when out-of-band isn't responding...that's the first place to let go of taps.
Then I just start chopping taps until I reach acceptable intersection of latency and SQ.
This has been much easier for me than developing a good IIR crossover for on and off axis....something I have yet to accomplish...
Here's a shot of the DIY60 using that approach. Latency is still high in the upper 20ms...but my tap axe is still swinging 
Best and thx, Mark
