Re: your vaulted ceilings, you might find an "acoustic cloud" solution. You can get one from Auralex that is an absorber (best used in front of the MLP:
and the pic you see in my virtual system is a cloud made from Acoustic Lens diffusors (best hung behind the MLP), I took 4 of them, connected them together in a row, then hung them from the ceiling with a kit: