A course with a unit or two on room acoustics but no practical experience. That would explain the over the top suggestion of needing an architecturally accurate model and professional level modelling software when the response is almost always dominated by simple room modes and placement with that simple knowledge, easily modelled with basic SW will get you far further than guessing. Microphones/SW will tell you how you are doing or present state.
In regards to your sub setup, unless you already have an exceptionally well treated room for bass, a FL, FR, C sub setup, whether floor, listening height, or otherwise makes no sense at all for cancelling room modes. If anything, it is going to make the bass much worse and really stimulate some modes. If you are going to go with the cost of 4 subs, I would be integrating LFE output with music bass management and optimizing overall placement. The subs don’t all have to match perfectly for room mode cancellation.
In fact your whole comment about your stereo system not needing subs to reinforce bass (only a small part of why you should use multiple subs) but your multichannel setup having multiple subs in less than optimal positions is strange..
I won’t say more but will leave to other readers to reach their own conclusions.