As I know, UK version X5 has no Amp. I never see X5 without Amp and I am not familiar to this system.
As I see on WDS, front mid-range and front speakers are feeded from same radio pins, so maybe there is some crossover.
If no-one can confirm this, I suggest to install in front doors JBL GTO607C component system.
Speaker size are : front and rear doors 6.5". Almost no modification needed.
Dash speaker size is 2", maybe 3" can fited.