OK, so messing around plugging and unplugging the HDMI cable from the DisplayPort convertor and bang.
It picks up the sound and can see SAMSUNG for HDMI 0
LibreELEC:~ # aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Generic [HD-Audio Generic], device 3: HDMI 0 [SAMSUNG]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 7: HDMI 1 [HDMI 1]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 8: HDMI 2 [HDMI 2]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 9: HDMI 3 [HDMI 3]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Generic_1 [HD-Audio Generic], device 0: ALC256 Analog [ALC256 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
But after a reboot back to no Sound
LibreELEC:~ # aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Generic [HD-Audio Generic], device 3: HDMI 0 [HDMI 0]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 7: HDMI 1 [HDMI 1]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 8: HDMI 2 [HDMI 2]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 9: HDMI 3 [HDMI 3]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Generic_1 [HD-Audio Generic], device 0: ALC256 Analog [ALC256 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0