@libremax I'm glad to confirm that BT music player does perfectly work on both systems (Ford Sync + Seat media).
Sound's just perfect.
Notice: "Unknown artist + unknown track" are displayed on both screens. But this doesn't really matter to me.
So, to resume: On both systems:
. BT initial pairing
. Auto pairing
. Contacts synchronization
. Coverage signal shown on the car screen
. Name of the device well displayed
. Outgoing / incoming calls
. Vocal command
. In car microphone + High speaker
. Phone volume adjustment
. Music via Bluetooth on the car radio
. Auto swap in call mode
. Battery status display
. In music mode: Displays the track being played
. Phone calls: Loud background noise covering much of the speaker's voice (recipient hears well)
Hope I've been this time clearer on my description