^ There's no such thing.  It's a nonsensical claim.  At least it you take it seriously.  It makes more sense if you don't and apply a relative context rather than absolute standards.

Probably the worst thing is when people ask:

Q - What does it sound like?
A - It sounds like nothing.  (it's wire w/ gain, totally transparent, yada yada)

Probably the worst thing is when people ask:

Q - What does it sound like?
A - It sounds like nothing.  (it's wire w/ gain, totally transparent, yada yada)

Yeah, you know me and I assume you are riling me up.

A: It sounds like nothing. (it's wire w/ gain, totally transparent, yada yada)
Purrin: Fuck you.

I've heard "wire with gain" attributed to amps with these characteristics (it's all over the place)

• Amps designed by disciples of Douglas Self.
• Polite sounding solid state amps.
• Strident and nasty solid state amps. <-- somewhat common usage
• Sterile and boring/flat solid state amps. <-- most common usage.

Every time, I hear "wire-with-gain", I tend to assume either bright or boring (as in committing errors of omission.) Ultimately the term is a cop-out and doesn't mean anything.

Sounds like it's kind of the "revealing" of the amp world.  Anytime someone says a headphone is revealing what they really mean is that it's bright and resonant.  Switching the word around is more accurate.  The bad recording is revealing the colorations of the headphone. 

In fact, anytime someone even talks about recording quality when they're talking about a headphone, they have colored headphones.