Absorb or Diffuse in between speakers?

>>Absorb or Diffuse in between speakers?

I would say that it depends on the speakers and on your room. As a rule of thumb, I usually absorb between box speakers and diffuse between dipoles and bipoles. But again, it depends on your room.

Rather than blind testing, I would suggest that you spend a little time and a very little money and perform an analysis on your room. I know that this seems like less fun than just blindly buying a bunch of treatments, but it will almost certainly result in better sound.

Both GIK Acoustics and RealTraps have posted a lot of free advise on their web pages. Start here: RealTraps - Room Measurement Series

and here: RealTraps - Acoustic Articles

It's really not at all hard to do, once you understand the basics, and will definitely result in the best result.

>>Omnis diffuse naturally and save having to deal with directional issues for the most part.

Again, it depends on your speakers and your room. I have had some "omnis" that required nothing behind them. My Apogee panels and ribbons, on the other hand, were very hot off of the rear wall and sounded much better with a considerable amount of diffusion behind them.

>>Did you mean absorption behind Apogees that were hot off the rear wall?

Nope. In this case, diffusion worked best. This was a large-ish room, and absorption overly damped (deadened) that end of the room response.