Here is a site you may want to look at:
http://www.zaphaudio.com/nondomes/
He does a lot of driver testing and is pretty well respected in terms of his knowledge of drivers and DIY designs. Be prepared though, he's not of the "audiophile" camp and pretty much wants to attibute what he hears to what he measures. That can irritate some folks. Still, knowledge is valuable and he does present some interesting data.
I'd be careful with tweeter swaps. There are a few things working in your favor. I don't know the PMC's very well, but if they are truly active to all drivers with no passive components you might stand a chance of this working out. Not sure how much tailoring is possible. Also, your highish x-over point is working in your favor as ribbons get ever more unhappy the lower you cross them.
The big hurdle will be making this mod look halfway decent. You are going to have to move the tweeter center up because you can't center them in the current hole or you'd need to cut into the midrange driver. Moving them up means some trickier woodworking will be needed to make good round holes (or rectangular) in the new locations.
Also, since you are now increasing the center-to-center spacing you will change some of the interaction with the midrange. This may or may not mess with the resulting sound. (That's the reason they cut into the midrange flange in the first place when they designed these things. The higher the x-over point the closer together the drivers need to be for good integration.)
http://www.zaphaudio.com/nondomes/
He does a lot of driver testing and is pretty well respected in terms of his knowledge of drivers and DIY designs. Be prepared though, he's not of the "audiophile" camp and pretty much wants to attibute what he hears to what he measures. That can irritate some folks. Still, knowledge is valuable and he does present some interesting data.
I'd be careful with tweeter swaps. There are a few things working in your favor. I don't know the PMC's very well, but if they are truly active to all drivers with no passive components you might stand a chance of this working out. Not sure how much tailoring is possible. Also, your highish x-over point is working in your favor as ribbons get ever more unhappy the lower you cross them.
The big hurdle will be making this mod look halfway decent. You are going to have to move the tweeter center up because you can't center them in the current hole or you'd need to cut into the midrange driver. Moving them up means some trickier woodworking will be needed to make good round holes (or rectangular) in the new locations.
Also, since you are now increasing the center-to-center spacing you will change some of the interaction with the midrange. This may or may not mess with the resulting sound. (That's the reason they cut into the midrange flange in the first place when they designed these things. The higher the x-over point the closer together the drivers need to be for good integration.)