My A4Q is the non-Bose, standard-stereo US version.
What's currently there: each front door has a 4" driver mounted low, with a 3/4" tweeter mounted high and crossed over with a simple capacitor. Speakers are made by Nokia.
Interestingly, the 4" driver on the driver's side is different from that on the passenger's side. It's a dual-voice-coil design, with the second coil fed from a seperate pair of wires. The reason for this is that the second coil is used for the speaker-phone (hands-free) output for the factory cellular phone. It's worth noting this for those who might use the factory phone, and then replace their speakers! Also bizarre is that the wire to the left set of speakers is a thicker gauge than the wire for the right speakers. I just taped off the wires that fed the second voice coil.
To get at the speakers, you have to remove the door panels. Remove the two visable screws at the upper corners of the door panel. Remove the screw in the armrest, inside the grab-handle area. Now remove the oval-donut trim piece that this screw was holding inplace, by snapping the trim piece downward. This will expose two screws; remove them. The door panel is now removed by lifting it upwards, then out. You'll need to disconnect electrical cables and unhook the door latch cable.
The tweeter is held in place by a wire clip; to remove the clip, you have to first remove the trim piece that contains the tweeter assembly and door latch handle. Do this by removing the screw in the back of the door panel between the tweeter and the latch, then pressing the two locking tabs (located forward of the tweeter) rearward, allowing the trim piece to be pushed outward. Now remove the wire clip from the tweeter by pulling the forward end of the wire out of the mounting hole.
The midbass drivers are held in place by three screws in a non-standard way. If you want to replace these, you'll need to build your own bracket. The stock speakers are very deep for 4-inchers, enough that a normal set of 5.25" drivers might fit in the same depth; BUT, the grill cut-out is 4" in diameter, mounting would be more difficult, and it's actually doubtful that you'll be able to fit them not because of depth, but because of room around the door frame.
I replaced the stock speakers with a Polk MM-3045 4" driver/ 1" tweeter component system, if anyone's interested.