Sounds like you will figure it all out Paul. I like using diffusors as well. The T-Fusors and MetroFusors by Auralex do a great job as well.
My solution to beautiful soundstage and no bass, why, add a couple of subwoofers of course. That way you can set the mains up where they sound the best, then add the appropriate sub Woof Woofers.
If you have not tried subs in your system, (I know Paul has!) I’d recommend JL Audio or Legacy Audio subs.
Either one can get your system rolling.
It must be a dilemma!
John Dunlavy preferred placing speakers along the long wall and also separated them wider than what would be an equilateral triangle.