Questions for the Head Fi Brigade

I'm thinking about getting myself a pair of headphones to achieve 2 different objectives:

1. To be able to listen to music with decent SQ late at night/early in the morning and not disturb my neighbours
2. To have a better sounding, more comfortable pair of headphones while away from home.  I'm interstate or overseas on a very regular basis and my current rig is a pair of PSB Audio M4U2's being driven by an Astell & Kern AK100.  While these work well on a flight, after a while they become uncomfortable and they are a LONG way behind the SQ of my speakers.

I'm looking at Sennheiser 600HD, 650HD, 700HD, Hifiman HE 560 and Mr Speakers Alpha Dogs.  I've auditioned the Sennies and the 560 so far.  The 560 is my favourite overall - mainly in terms of comfort, but also its sumptuous midrange.  The 700's were my fave for jazz, but the 560's were nicer with rock and electronic tracks.  The 600's aren't out of the picture - they're heaps cheaper and they're not giving much ground to any of the others I've tried so far.  Easily the pick in terms of bang for buck.  The 650's were a bit dark for my taste. I'm looking for a pair of cans I can keep on my head for hours on end and still be comfortable. 

So, a few questions for the head fi brigade here:

• Are there any other headphones - ideally under the $500 bracket (I'm happy to look at second hand options) - that I should be auditioning?  
• Is it possible to plug a device into my Manley Stingray integrated amp that I can plug my headphones into (using the Stingray as an amp to drive the headphones)?  Will such a device have as good a SQ as a dedicated head amp?
• My  experience with each of these headphones is that the AK100 struggles to drive them and lots of detail just vanishes.  Is there a good quality portable head amp that won't break the bank (ideally not much bigger than a mobile phone and under $200), or am I dreaming?
• Is it possible to get headphones that provide a realistic soundstage?  I keep reading reviews about headphones that provide an amazingly large soundstage, but having listened to everything from HD800's, LCD2's and LCD3's, I'm beginning to wonder whether the reviewers making these claims have heard a decent pair of speakers.  The soundstage on all of these high end cans sounds so much more constricted (smaller) and less lifelike than my speakers it's not funny.

I would be grateful for any help/feedback you can provide.