First, in the Feature Requests thread you said you wanted to sort by release Date, so that is what I wrote about in that thread, and then moved that answer here. See last paragraph for sorting by Data.
Create a new Custom Preset sort order for "Sort Inside Groups By" in Standard View, to be used in when modifying the Theatre View View. Name it appropriately. I just used "Date (release)" since we are sorting by the field [Date (release)] and sort it "a-z". See first image.
Then modify the Artist View in Theatre View to sort Albums by this new Preset, instead of just "Ascending" Order. See second image.
PS: I am assuming that you want to sort by the field [Date (release)] that you have populated. Normally the [Date] field is populated when a CD is ripped, and there are already two options to sort within Groups using that field, "Date (newest first)" and "Date (oldest first)".