Avalon Isis Advice needed

Not sure if that would work. The bass output on the Isis is substantial. Have you considered the Avalon Time or Eidelon Diamond perhaps? Your room would need some very heavy treatment to deal with waves bouncing around.

If you sit 15 feet away from these speakers with only 6 feet of separation, your soundstage will probably be very distant and uninvolving.

I agree with emailing/calling Gary Mulder at Avalon. He has experience setting these up. Send him photos. My dealer had the Isis in a smallish room, and he did some major treatments to the walls.

It might work if you are willing to sit closer to the speakers, 10ft or less. If you have the option, experiment moving a subwoofer close to the side wall without equalization and measure frequency response at potential sitting location. If you can get a reasonable bass alignment, Isis may work.

That may work, but you may want to sit more near field than the 15 feet you specify. I'd say around 8 feet, or more than the 15 feet, but your results will vary with your expectations and preferences. As with all Avalons, the farther you pull them out into the room, the deeper the sound stage. I'd also consider firing them straight with no toe in, they tend to get more confusing with toe in (I read in a magazine recently an explanation why this is a preferred method, but I can't recite it- something to do with phase coherency- in any case I prefer them firing straight).

While they possess significant bass, I think it is quite balanced, and true to Avalon's usual excellent presentation. I don't think they're anywhere near as difficult to tame as many other large speakers in that regard. They require more juice to "open up" than the Eidolons (an amazing thing the Visions and Diamonds do is have an almost perfect tonal balance at a sound barely above a whisper). That's not to say they have to get loud to be balanced, just that the Eidolons balance tonally almost immediately, whereas the Isis tend to need to get a few watts burning for them to show their impressive abilities. But the other side of the coin with them needing to open up a bit, is that they have almost no appreciable strain at up to silly levels of playback. The presentation is also high, so an extremely short listening chair will not work well with them.

Gary Mulder is no longer at Avalon to my understanding, so you'll need to talk with the new rep. or with Lucien.