Okay, I am throwing this out there… I THINK I have / had the same problem you are dealing with (again, I think) and may have figured out a solution? Sorry if this is a waste of time… So, I wanted the shortcode to immediately show my main category with all of my subcategories because as you said the index was totally boring, non-descriptive etc. So, I found the numerical ID in the URL of the category (a ### three digit number, mine happened to be 309) and plugged that into [bbp-single-forum id=309] and that worked? So, now when I navigate to that specific page, it automatically opens up to the main + sub category view and not the index view. Again, apologies if this was a waste….
