I'd say try your Mirages in the new room first. You might need to diffuse the rear-firing drivers' radiation somewhat if the wall is too close.
As far as how many "ways" a speaker should have, I look at other things first. How many "ways" is a design choice that involves tradeoffs, and there are exceptions to most of the generalities that can be raised. However since you've narrowed your choices down to what your local dealer carries (and I think that's great that you're committed to supporting him), the theoretical merits of two way vs three way is of academic interest only.
Instead, let's do some listening! Your own ears are far more reliable than the consensus opinion of this or any other audio forum.
My premise is that the speaker that's the most enjoyable long-term is the best speaker. In pursuit of such, you might try these techniques:
1. Listen at very very low volume level - down at the threshold of audibility. Do you still get good clarity? Is the midrange still enjoyable? You won't hear the bass and will hear but little treble, so this technique sort of throws a spotlight on any midrange anomalies that might otherwise go unnoticed in a brief listening session but become distracting over the long haul.
2. Turn the volume level up louder than normal, and see if it gets harsh. The ear is more sensitive to colorations that give rise to harshness at high volume levels than at medium or low volume levels, so this technique is designed to reveal such colorations more quickly than low or medium volume listening would.
3. Leaving the volume level up louder than normal, get up and walk outside the room but leave the door open. Now all you can possibly hear is the reverberant field. If the speaker sounds convincing from the next room that means the reverberant field is smooth (which is very good for long-term listening enjoyment) and it probably means that the dynamic contrast is also good (which once again is great news).
Listening at a variety volume levels can help reveal whether or not the tonal balance changes significantly with volume level. Manufacturers almost never talk about this, but it happens a lot more often than we'd like to admit.
Take into account your normal listening habits as well. For instance, do you sit in the sweet spot only, or do you (or other listners) often sit outside the traditional sweet spot? If the latter, then obviously you want a speaker that sounds good across a large arc (in general, a three-way with a dome midrange or small diameter cone midrange will sound more uniform across a large arc than a typical two-way).
Finally, go back home and try these test on your Mirages - you may be surprised. You may find that in some ways these new speakers are more of a step sideways (or maybe even backwards) than a step forward. I say this out of respect for the Mirage design.
Best of luck in your quest,
Duke
dealer/manufacturer
