Ricred,
Re my initial suggestion to getting speaker first is none other than that from previous experiences, different speakers usually do require different treatments--optimally.
If modular units--still ok, you might just need to add, subtract, or simply move them around. However, if fixed/built into room--then not so easy, more headache should you later decide to switch speakers. Hence for me, whenever possible, always better to get a fixed on designated speaker first, then specifically treat room around it. As in your case : what Sasha requires might differ from that of Sophia's.
But at the end, either ways, whether it be room/speaker first--some corner bass traps, front wall, and sides' first reflection absorb/diffusers are basic essentials which will definitely reap benefits in almost any room.
Also, if you go modular--your ears, with some dealer's help (basic measurements) can do, no need Rives etc. Only if you plan on built-in ones incorporating some sort of room re-design, then those pros will come in handy, ime.