[manbear]

Air is not interchangeable with instrument separation and imaging.

Yeah, I said that too. They are different.
 
My issue is that I don't know what the "air' between instruments actually sounds like, and I think half the people who use the term don't know what it sounds like either or are using the term differently. 

For example, if the Q701 doesn't have air, then it should be congested, right? Since airy and congested are opposites. Yet IMO the Q701 is not congested at all. 

Still IMO, congested and separation are opposites. The Q701 has great separation, though its imaging lacks depth. 

The basic problem is that people should try to actually describe what they hear, instead of just using these terms. 

 

[davidsh]

Congested isn't the opposite of airy IMO.
Try reading darth nuts review of the 007, great explanation and insight.
Glossary: http://www.head-fi.org/t/220770/describing-sound-a-glossary

 

[Valhallatier]

  While reading some reviews, I ran into the following paragraph from this link (Headfonia - Old School Trio) and I think it describes very well what "air" is.
 
 
Hope it helps!

OMG
that helps a LOT!
thanks!