I have found a bug with Tinkerboard which prevent usage of S/PDIF and passthrough.
The long story can be found in armbian forum:
For short description:
The command "aplay -L|grep iec958" will present "iec958:CARD=OnBoard,DEV=0" but the "DEV=0" must be "DEV=1"
An workaround can be easily added to the (in LE for tinkerboard) already modified file "/usr/share/alsa/cards/USB-Audio.conf".
The workaround is:
1.) copy the original (unmodified) section of above file at the end of the file (original is present in ubuntu, gentoo, armbian, volumio)
2.) enable the second device with a number <>999 (e.g. 1) and disable the first one with "999" instead of "0" (sections "USB-Audio.pcm.iec958.#" at the end of the file)
The result of the added section should be look like this (but better formatted 
)
Display Spoiler
<confdir:pcm/iec958.conf>
USB-Audio.pcm.iec958.0 {
@args [ CARD AES0 AES1 AES2 AES3 ]
@args.CARD { type string }
@args.AES0 { type integer }
@args.AES1 { type integer }
@args.AES2 { type integer }
@args.AES3 { type integer }
@func refer
name {
@func concat
strings [
"cards.USB-Audio."
{ @func card_name card $CARD }
".pcm.iec958:CARD=" $CARD
",AES0=" $AES0 ",AES1=" $AES1 ",AES2=" $AES2 ",AES3=" $AES3
]
}
default {
# FIXME: we cannot set the AES parameters
type hw
card $CARD
device {
@func refer
name {
@func concat
strings [
"cards.USB-Audio.pcm.iec958_device."
{ @func card_name card $CARD }
]
}
default 999
}
}
}
USB-Audio.pcm.iec958.1 {
@args [ CARD AES0 AES1 AES2 AES3 ]
@args.CARD { type string }
@args.AES0 { type integer }
@args.AES1 { type integer }
@args.AES2 { type integer }
@args.AES3 { type integer }
@func refer
name {
@func concat
strings [
"cards.USB-Audio."
{ @func card_name card $CARD }
".pcm.iec958_2:CARD=" $CARD
",AES0=" $AES0 ",AES1=" $AES1 ",AES2=" $AES2 ",AES3=" $AES3
]
}
default {
# FIXME: we cannot set the AES parameters
type hw
card $CARD
device {
@func refer
name {
@func concat
strings [
"cards.USB-Audio.pcm.iec958_2_device."
{ @func card_name card $CARD }
]
}
default 1
}
}
}
After the change you cant test the result by:
alsactl init
aplay -L|grep iec958
iec958:CARD=OnBoard,DEV=1
For the normal user this is not so simple because the read-only file system.
Who of the tinkerboard developers could do this permanently?