Absorption, Diffusion or a combination of it all?

@drbond - Have you tried diffusion behind your electrostatics? I started out with GIK Alpha Absorber/Diffusors behind my dipole speakers and was not happy with the soundstage and liveliness of the music. I switched to ATS Quadratic Residue Diffusors and really like the change (as did my audiophile friends). 

Of course, every room is different, and not everyone has the same preferences in sound presentation. But I've generally found manufacturers of dipole and open baffle speakers to recommend diffusion behind the speakers. I had thought that the GIK panels would have worked ok but they were sucking too much of the life out of the music.

As with everything else in this hobby, it takes a lot of experimentation to get the best results. You can get a head start by hiring an experienced acoustician to come an evaluate your room and provide recommendations, but your personal tastes need to dictate the final solution. 

It's relatively easy and inexpensive to experiment with absorption since low cost fiberglass or rock wool panels can be purchased from your local home-improvement store (Lowes, Home Depot, etc.), or you can just use spare blankets, pillows, quilts, etc. 

Diffusion is a bit more challenging since good diffusors are somewhat costly. I haven't found the cheap diffusor panels to be that effective.

But once you get it reasonably dialed in, acoustic treatments provide a LOT of bang for the buck. 

@ozzy - I'd leave the tube traps in the corners. I like the ATS QRDs. I wrapped these with Guilford of Maine cloth and they look quite nice, but you might prefer the wood look. See my virtual system page to see how they look with cloth wrap. I have 4ft wide floor to ceiling diffusors behind the speakers. 

I think the Vicoustic Multifusors are also pretty nice if you prefer the look. These are deep enough to provide fairly wide band diffusion. 

@ozzy - I'd recommend trying the planar speakers with your current room acoustics setup to start with and see what you think. I've found that I prefer diffusors behind my dipole speakers without any absorption, but every room is different and some people have found they prefer absorbing the much of the backwave. 

After getting them set up, I'd try removing the Stillpoint panels behind the speakers and seeing if you like the sound better. If so, this probably points to switching to pure diffusors.

@ozzy - are you planning to use subwoofers with your planars? The bass generated by dipole speakers is a lot different than a typical box speaker since it doesn't pressurize the room like a box speaker. In my opinion, this results in more natural sounding, and very nuanced bass. 

A dipole speaker will have nulls in the low bass response to the sides of the panels since the front and rear waves cancel at that point, so the side to side and floor to ceiling room modes are not excited the way they are with box speakers.

I am using DIY bass traps that are similar in construction to the Tube Traps and I have found the bass to be very articulate and natural sounding. But in my room with my system (dipole woofers that reach down to below 20Hz), I haven't found that the bass traps make all that much difference. They do smooth out the bass a touch, but it's a fairly subtle effect. Using REW to measure the room response, I don't see a huge difference (although the response is a bit smoother with the bass traps).

It's possible (maybe even likely) that the ASC tube traps work a bit differently than my DIY solution, but I'd give them a try before making any decisions to change things.