Success at last!
CSM is turned off, UEFI boot only.
I edited the 2nd partition, replaced the extra and extra2 with the driver extension ones, burned the image again and now i was able to get network connectivity.
At first attempt it just booted up like my old diskstation, i had to select "Restore diskstation" in the Find.synology.com - This brought my old config back but all my data drives had "System partition" warning on them.
Rebooted and this time selected the "reinstall" option in the USB, found it in find.synology.com and this time i could select migrate first, and then either keep settings or reinstall.. I selected reinstall and it formatted etc, but when it uploaded the manually downloaded file it failed with "File is probably corrupt" - But i know for a fact its not.
Rebooted again, this time selecting the normal boot option, again i could find it in find.synology.com and had the migration option again, and for some reason the reinstall procedure worked here, it accepted the same file as i tried before and the diskstation is now successfully re-installed on the new motherboard, and the 10GBe is functioning
Thanks a bunch guys @IG-88 and @flyride