DM800HD/DM800HDse/DM800HDseV2/DM500HD/DM8000HD :You can install the v6 images but then you will need your Japhar Sim to be upgraded to OS v6 if not already upgraded, you can upgrade your sim easily with the Plugin JAM 5.x, selecting first option "Japhar addons Manager" and option "Japhar Sim Card Flashing DM-BOX-MODEL v6". It will upgrade your sim with 2 reboots (it can easily take 5 minutes) and you will be able to use all images v3,v5 up to v6.
Only for DM800HDseV2 :Previous Images v5 will not be SSL and driver compatible so you will need to replace the driver-v5 by the driver-v6 as well as flash the SSL89-v6 if you want to use an old v5 image with Sim Japhar OS v6 (SSL89-v6 will boot with v5 and v6 OS Japhar Sim).