You want to have a technical rules discussion?
The Item creation rules are very specific on how MM are added to a spell effect. You are trying to add DMM to an item, but DMM does not modify the spell effect, it modifies how the MM spell level adjustment cost is paid. Item creation rules already have rules about how MM spell level adjustment cost is paid for. And it does not include DMM in thoes rules.
Further, the spell source for a magic item does not matter. You can use a SLA, scroll, or any other source. The source has no effect on the items spell effect. For example if it came from a scroll, it is not treated as a "scroll" when cast. So I do not see how you are justifying the spell source coming from DMM having an effect on the spell effect in the item.
Did i miss something?