Zyxel NSA310 - Network Adapter missing - Newbie needs help! (no replies)

Hello all,
I've been trying to re-use my old Zyxel NSA310 with u-boot, Debian and OMV as application (open media vault). First attempt was not succesful, I had to start from the very beginning again. I've managed to install u-boot now and Debian - so far so good.
BUT: There is no network adapter present, which isn't really helpful :(
Here's some info:

U-Boot 2017.07-tld-1 (Sep 05 2017 - 00:54:15 -0700)
ZyXEL NSA310 1-Bay Power Media Server
SoC:   Kirkwood 88F6281_A1
DRAM:  256 MiB
WARNING: Caches not enabled
NAND:  128 MiB
In:    serial
Out:   serial
Err:   serial
Net:   egiga0
PHY reset timed out
MV88E1318 PHY initialized on egiga0
Hit any key to stop autoboot:  0

NSA310> printenv
arcNumber=4022
bootargs=console=ttyS0,115200 root=LABEL=rootfs rootdelay=10 orion_nand:0x100000(uboot),0x80000(uboot_env)
bootcmd=run bootcmd_uenv; run scan_disk; run set_bootargs; run bootcmd_exec
bootcmd_exec=run load_uimage; if run load_initrd; then if run load_dtb; then bootm $load_uimage_addr $load_initrd_addr $load_dtb_addr; else bootm $load_uimage_addr $load_initrd_addr; fi; else if run load_dtb; then bootm $load_uimage_addr - $load_dtb_addr; else bootm $load_uimage_addr; fi; fi
bootcmd_uenv=run uenv_load; if test $uenv_loaded -eq 1; then run uenv_import; fi
bootdelay=10
bootdev=usb
device=0:1
devices=usb ide mmc
disks=0 1 2 3
dtb_file=/boot/dts/kirkwood-pogo_e02.dtb
ethact=egiga0
ethaddr=fc:f5:28:76:ae:de
if_netconsole=ping $serverip
init_ide=ide reset
init_mmc=mmc rescan
init_usb=usb start
ipaddr=192.168.0.231
led_error=orange blinking
led_exit=green off
led_init=green blinking
load_dtb=echo loading DTB $dtb_file ...; load $bootdev $device $load_dtb_addr $dtb_file
load_dtb_addr=0x1c00000
load_initrd=echo loading uInitrd ...; load $bootdev $device $load_initrd_addr /boot/uInitrd
load_initrd_addr=0x1100000
load_uimage=echo loading uImage ...; load $bootdev $device $load_uimage_addr /boot/uImage
load_uimage_addr=0x800000
mainlineLinux=yes
mtdids=nand0=orion_nand
mtdparts=mtdparts=orion_nand:0x100000(uboot),0x80000(uboot_env)
mtparts=mtdparts=orion_nand:0x100000(uboot),0x80000(uboot_env)
preboot_nc=run if_netconsole start_netconsole
scan_disk=echo running scan_disk ...; scan_done=0; setenv scan_usb "usb start";  setenv scan_ide "ide reset";  setenv scan_mmc "mmc rescan"; for dev in $devices; do if test $scan_done -eq 0; then echo Scan device $dev; run scan_$dev; for disknum in $disks; do if test $scan_done -eq 0; then echo device $dev $disknum:1; if load $dev $disknum:1 $load_uimage_addr /boot/uImage 1; then scan_done=1; echo Found bootable drive on $dev $disknum; setenv device $disknum:1; setenv bootdev $dev; fi; fi; done; fi; done
scan_ide=ide reset
scan_mmc=mmc rescan
scan_usb=usb start
serverip=192.168.29.1
set_bootargs=setenv bootargs console=ttyS0,115200 root=LABEL=rootfs rootdelay=10 $mtdparts $custom_params
start_netconsole=setenv ncip $serverip; setenv bootdelay 10; setenv stdin nc; setenv stdout nc; setenv stderr nc; version;
stderr=serial
stdin=serial
stdout=serial
uenv_addr=0x810000
uenv_import=echo importing envs ...; env import -t $uenv_addr $filesize
uenv_init_devices=setenv init_usb "usb start";  setenv init_ide "ide reset";  setenv init_mmc "mmc rescan"; for devtype in $devices; do run init_$devtype; done;
uenv_load=run uenv_init_devices; setenv uenv_loaded 0; for devtype in $devices;  do for disknum in 0; do run uenv_read_disk; done; done;
uenv_loaded=0
uenv_read=echo loading envs from $devtype $disknum ...; if load $devtype $disknum:1 $uenv_addr /boot/uEnv.txt; then setenv uenv_loaded 1; fi
uenv_read_disk=if test $devtype -eq mmc; then if $devtype part; then run uenv_read;  fi; else if $devtype part $disknum; then run uenv_read; fi;  fi
usb_ready_retry=15
Environment size: 3135/131068 bytes

During boot, Debian reports that egiga0 ifup fails. Based on the information I have, the correct name should be "enp1s0"

root@debian:~# ifconfig -a
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 12  bytes 1710 (1.6 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 12  bytes 1710 (1.6 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

My (newbie!) assumption is that the u-boot image file does not match with the hardware (r8169)? I found some threads regarding this subject, but nothing really helped.

Has anyone any idea? I'm grateful for any support I can get!
Thanks very much!
Marc