I know a bit about the 18 expedition audio setup as I researched it already for an XLT upgrade.
For XLT upgrade to B&O,
Even in the B&O thet sync head unit is still powering some of the speakers and the amp is powering some others. It's not all coming out of the amp. Some speakers are special and some are standard Ford parts.
To upgrade a XLT it's likely (I haven't done it, but this is pretty accurate)
- left/right rear pillar panels to house the rear back speakers which don't exist in the XLT.
- left side rear panel to house the sub. The XLT one doesn't work since there is a pocket storage where the sub goes.
- B&O sub
- B&O amplifier
- upgraded receiver module with a2b output.
- a2b split Y harness to tap into and run some lines without redoing Headunit wiring
- a2b wiring
- extra wiring for back rear speakers.
- replacement speakers for the ones that are B&O specific.
- B&O center grill for aesthetics
- reflash / config on stereo to enable a2b feature output
- power wiring for amp and fuse entry on fuse box
Even when someone did an upgrade of their limited, they may only have a few parts for someone else to use in an XLT since the two are really different.