Hi there,
You are doing nothing wrong. I had the same problem myself. It took Meridian 5 months to solve this problem for me. You have to ask them for new g68 software 1.16 or above and you also need the new configuration program version 1253 which solves the problem. If you just install the 1.16 software it wont be enough because the current configuration program has a glitch in it when you store your setting with a rear sub.
Hope this helps.

G68ADV, HD621, G98DH