Some thoughts on soundstage:
On one extreme, my custom IEM sound exactly like they look - like little wads of silicone plugged into my ears. The sound seems to eminate right at my ears or maybe an inch outside of that. Instrument placement is nice between those two points.
On the other extreme, my Qualia 010, especially when I've been listening for a while, try as I might, it just doesn't sound like the sound is coming from drivers an inch outside of my ears. It's like someone plugged in a neural jack and bypasses my ears and feeds audio sound directly into my brain. With that, the sound has a presence outside the physical limitations of normal headphones.
On a scale of 1 - 10, with the IEM at 1 and Qualia at 10, the Grado RS-1 are at a 2.5 for me. Narrow soundstage. Much nicer than the IEM, because it doesn't sound like the sound's wadded up in my ears. It's got a bit of air to them, but it's very clear the sound is coming from drivers resting gently on my head, and doesn't go beyond that. The soundstage sounds like I'm listening to regular headphones.
Sennheiser HD600/650 are maybe at a 7 to me. The sound sounds more like it's coming from the air around my head than the headphones, but the illusion is not nearly as complete as the Qualia. The soundstage stretches significantly beyond that of average headphones to me.
PS-1 is somewhere better than a RS-1 but not as good as a HD600/650. My understanding is that the PS-1 is the Grado with the best soundstage. It sounds like a normal headphone with very good soundstaging.
AKG K 1000 on the other hand - the soundstage is narrower than the Qualia, but it is incredibly coherent. The panorama goes clearly left to right, but doesn't reach all the way to the walls. The Qualia soundstage is clearly artificial - jacked straight into the brain. The AKG K 1000 reconnects with natural physical hearing, even if it's reach is more narrow.
Best regards,
-Jason