I personally don't think 6-8" from the wall is a problem for rear ported Omegas. They generally do well near a wall, and are overall an easy speaker to place in a room so long as the acoustics aren't completely out of whack. A few years back I had Louis custom build me a set of small front ported speakers (4.5 HempCone driver) for on a mantle. They sounded typically Omega good, but had little bass. I pulled them out and put some Super 3i (HempCone 4.5) in their place with the rear port not more than an inch from the backing wall. Everything now fleshed out with a nice bass - a much more enjoyable listen. I'm not a bass head, but if a speaker has any anemia in the lower mids/bass area it loses my interest. Any Omega is a master of tone, but of what I've heard of the Omega line, the Alnico wins out.
As far as speaker placement, room size, and acoustics go, yes, they can have huge effect on the quality and quantity of bass output. However, source and amp can have a huge effect on the quality/quantity of bass. I've had a particular DAC for 7+ years that just can't be beat in the bass department and when it's in the system I get the best bottom end regardless of Omega down line. A SET with it's lower damping factor could be more of a problem with speakers close to a wall than a solid state amp with it's higher damping factor and greater control over the speaker driver.