If I understand your question right:

It is possible for quite some time (I don't remember when it was introduced) to have multi disc sets consisting of 2 different types of disc. I have 12 of these sets in my collection. For each disc in the set you can choose the right Album icon on the Misc tab of the Record properties.
The icon of the first disc is shown for the set, so you can diffentiate between a DVD set with a bonus audio CD or an audio CD with a bonus DVD.
I have entered 1 format for these sets: CD & DVD, but you can choose any format you want.

Is this an answer to your request? This is the way I organize these combinations and it works fine for me.