rEFInd and GRUB messups of NuTyX under BtrFS

I have NuTyX installed on a BtrFS subvolume, and have tried auto rEFInd and GRUB-EFI, but were failed, and i'm unsure how to assign the volume argument for manual rEFInd entry as below,
Code:menuentry "NuTyX" {
icon /EFI/rEFInd/icons/os_NuTyX.png
volume ...
loader /NuTyX/boot/kernel-%v
initrd /NuTyX/boot/initrd-%v
options "root=/dev/sda6 rw rootflags=subvol=NuTyX"
}What to be entered for that argument? The main volume is on /dev/sda6 at Linux distroes, but unsure for its EFI shell volume name
And my kernels, initrd's, and partition layouts are below,
Code:bash-5.0$ l /boot /lib/modules $$ df
/boot:
total 116600
-rw-r--r-- 1 root root 97088111 Jan 20 00:31 initrd-5.10.6-NuTyX
-rw-r--r-- 1 root root 11875048 Jan 9 22:14 System_64.map-5.10.6-NuTyX
-rw-r--r-- 1 root root 10178560 Jan 9 22:14 kernel-5.10.6-NuTyX
-rw-r--r-- 1 root root 240350 Jan 9 22:14 config_64-5.10.6-NuTyX
drwxr-xr-x 1 root root 210 Jan 25 04:54 .
drwxr-xr-x 1 root root 110 Jan 20 04:27 ..
drwxr-xr-x 1 root root 92 Jan 25 04:31 grub
lrwxrwxrwx 1 root root 19 Jan 20 00:31 initrd -> initrd-5.10.6-NuTyX
lrwxrwxrwx 1 root root 19 Jan 20 00:31 kernel -> kernel-5.10.6-NuTyX
drwxr-xr-x 1 root root 0 Nov 2 21:22 efi

/lib/modules:
total 0
drwxr-xr-x 1 root root 4658 Jan 20 00:31 ..
drwxr-xr-x 1 root root 464 Jan 20 00:31 5.10.6-NuTyX
drwxr-xr-x 1 root root 24 Jan 9 22:11 .
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda6 btrfs 148G 92G 55G 63% /
udev devtmpfs 3.9G 0 3.9G 0% /dev
shm tmpfs 3.9G 0 3.9G 0% /dev/shm
/run tmpfs 3.9G 0 3.9G 0% /run
tmp tmpfs 3.9G 0 3.9G 0% /tmp
bash-5.0$