OK Martin, that image worked. I did a full install of Debian Stretch from it. Below is the output at the tail end of bootup and login.
----------------------------------------------------
Debian GNU/Linux stretch/sid backup ttyS0
backup login: root
Password:
Linux backup 4.6.0-1-marvell #1 Debian 4.6.4-1 (2016-07-18) armv5tel
----------------------------------------------------
The 0x600000 change also still continues to boot my existing Debian Jessie install.
Thanks for the work you do to keep these old pieces of NAS hardware working.
Mike