An online tool isn't going to have parameters for every single situation in a listening room--it would make their tool needlessly complex and require too much code to use online (it would not perform well in a browser, in other words). But if you fill out the basic floor plan in the visualizer and contact one of their advisors with the rest of the dimensions and/or send some photos, they would be able to recommend something based on that and whatever else you tell them. They have worked in all sorts of spaces (studios, presentation rooms, theaters, public spaces, etc.) aside from audiophile listening rooms.
@DC has an upper level with sloped portions of the ceiling (similar to our bungalow, where the upstairs bedroom has similar ceiling slopes) and it doesn't allow for that either. My situation is also somewhat unusual (a good portion of the wall opens into the kitchen) so there are all sorts of parameters happening here which require explanation beyond the visualizer.
FWIW, I've actually found it easier to lay out my room's floor plan in Visio using simple shapes--for me (experienced in Visio) it's a smoother and more intuitive experience. Not so much for sound treatment, but to find a way to rearrange the room so I can gain more space.