Booting Linux Kernel 4.4.133 Oxnas (OX820) Pogo V3 from SATA (no replies)

Hello,

I have followed the rootfs Instrauctions of
https://forum.doozan.com/read.php?2,16044
to transfer the Debian rootfs to an SSD..

I attached the SSD to my Pogoplug V3's SATA port and I am trying to boot now. I was hoping my uboot (U-Boot 2013.10-tld-4 (Sep 08 2014 - 19:43:38) for OXNAS) would detect it and simply boot - but it does not.

I searched now, if I need to change the boot parameters and I found:
https://forum.doozan.com/read.php?2,32994

However, I find this very confusing, and it implies, that uboot is not working correctly, right?

My parameters are:

OX820> printenv
autoload=no
baudrate=115200
bootargs=console=ttyS0,115200n8
bootcmd=run dt_bootcmd_usb
bootdelay=10
console=console=ttyS0,115200n8
dt_bootcmd_usb=usb start; run dt_usb_bootcmd; usb stop; reset
dt_bootm=bootm $uimage_addr $uinitrd_addr $dtb_addr
dt_load_dtb=ext2load usb 0:1 $dtb_addr /boot/dts/ox820-pogoplug-classic.dtb
dt_load_initrd=ext2load usb 0:1 $uinitrd_addr /boot/uInitrd
dt_load_uimage=ext2load usb 0:1 $uimage_addr /boot/uImage
dt_usb_boot=run dt_load_uimage; run dt_load_initrd; run dt_load_dtb; run dt_bootm
dt_usb_bootcmd=run usb_set_bootargs; run dt_usb_boot
dtb_addr=0x62c00000
ethact=mii0
ethaddr=00:25:31:02:AE:F5
if_netconsole=ping $serverip
ipaddr=192.168.180.19
mtdids=nand0=41000000.nand
mtdparts=mtdparts=41000000.nand:14m(boot),-(data)
ncip=192.168.180.44
preboot_nc=run if_netconsole start_netconsole
serverip=192.168.180.44
start_netconsole=setenv ncip $serverip; setenv bootdelay 10; setenv stdin nc; setenv stdout nc; setenv stderr nc; version
stderr=serial
stdin=serial
stdout=serial
uimage_addr=0x60500000
uinitrd_addr=0x60e00000
usb_device=0:1
usb_set_bootargs=setenv bootargs console=ttyS0,115200 root=/dev/sda1 rootdelay=10

Environment size: 1220/131068 bytes

Is there a setting I can apply, which makes uboot first check for SATA drives and then USB drives for booting?
Or a less confusing how-to?

Any help would be very appreciated.

Regards, Dieter

PS: I had more then one partition and changed that now to one ext4, only, but still:

scanning bus 0 for devices... 2 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found
** Bad device usb 0 **
** Bad device usb 0 **
** Bad device usb 0 **
Wrong Image Format for bootm command

Led:    ORANGE (Failed)

Update2: I put the SDD into an USB case, and it does not boot!

USB0:   USB EHCI 1.00
scanning bus 0 for devices... 3 USB Device(s) found
       scanning usb for storage devices... 1 Storage Device(s) found
** File not found /boot/uImage **
** File not found /boot/uInitrd **
** File not found /boot/dts/ox820-pogoplug-classic.dtb **
Wrong Image Format for bootm command

Led:    ORANGE (Failed)

I seem to have missed something?
Why is it searching for a dtb-file. Ithought, with my version of uboot, I should skip the generation of the dtb file?