The front door mids have a "tube" or "channel" that the speaker is mounted in the directs the sound towards the door panel - it does not mount directly to the inner face of the door. A 5.25 speaker will readily fit within this tube. Some 6.5 will also and some people have trimmed their 6.5's down to fit (if the speaker has a plastic basket). And yes, the stock amp has crossovers.

__________________
2001 X5 3.0i (PP/WP/AP) Traded at 213K miles
RARE White on Black - Why does everyone get Tan??
First E53 with 215s on XOutpost!!