While the mid dome used in the OB1i looks similar to the ATC one, the PMC version is inferior, I believe. There are two versions PMC make, a cheaper, simpler one and a better one that is used from the IB1i upwards IIRC. The latter is fine.in an audio magazine I have read that the OB1i with complex music, get problems with the representation and resolution.
I imagine that this kind of mid-range driver is not so easy to master. ATC used decades, in order to come to the current quality. My guess is that PMC is not yet on a level with ATC.
Is that just scribbling, or there is some truth?
Personally, I didn't get on with the OB1 (note: non-i). Don't know the current version.
What's wrong with your existing speakers?