[penguinicus]

I'm also a drummer and I can't praise the ASG-1.2s enough.  I have used them consistently since March for daily listening, travel, monitoring, and (with slight EQ) live engineering.  I've used Shure E2cs and Future Sonics Atrios for the same applications in the past and the ASG-1.2s have addressed every gripe I've had with accuracy, coherency, and durability.  The way they represent drums in particular is incredibly engaging - I would say they are made for it.  They are designed for musicians first, with large sound bores (easy to clean) and recessed sockets (resistant to tension, tugs, sweat).  Mine are still in pristine condition, aside from the unavoidable oxidation of the copper cable.
 
I haven't heard the HD600s, but I've auditioned the 518s and 558s.  If the HD600 is your preferred sound signature then the ASG-1.2s may be more bass-heavy than you'd prefer (though they are considered mid-centric), but their non-fatiguing highs will probably correspond well with the signature Sennheiser "veil".  They have a particular nub on top that causes discomfort after 4+ hours for me, but I understand that in the ASG-2s they have reduced this.  If you can't make the extra $200 for the ASG-2s instead, you may email Aurisonics and ask them if they have plans to change the shell on the ASG-1s to match the ASG-2s following their release.
 
I have enjoyed them enough that I have a pair of the AS-2 customs finishing manufacturing right now, including tuneable bass ports (which I know can be done right - see Future Sonics mg6pros) and ambient ports for self-monitoring at small venues (i.e. drums not mic'd, thus not in the monitor mix), and will be upgrading my ASG-1s to ASG-2s as soon as the opportunity is presented.

 

[ocharlas]

I like the idea of the ASG-1.2 (which as I understand is just the current incarnation of the ASG-1 correct?). it seems a bit different from the others with it's single dynamic driver and sealed/tough looking build.  From what I've read though it seems that they're a bit darker than I'm looking for.  For what it's worth, I don't consider the HD600's to be veiled, I actually love their treble - It's actually more detailed and forward than any other (quality) headphone I've (personally) ever heard.  But that's probably a list that's only about a dozen high end heaphones long.  
 
To me, real recessed highs are the Shure IEMs, which are the only IEM's I have ever heard - maybe except the E3's, but I haven't heard them in a long time.  
 
As far as the ASG-2s, I would love to check them out, except I know that when they come out they be too expensive, and I'm sure it'll take a little while for them to start showing up used for a decent price.  Plus, then I have to wait...that's the biggest dealbreaker.

 

[ocharlas]

I've got certain information, man...New crap has come to light...Quality IEMs, in the parlance of our times, you know...
 
Shootout time:  For *about* the same price I can get in the classifieds here the Heir 4.ai or the Westone 4R, both with very little use
 
or,
 
Earsonics USM3 v2, brand new
 
All these are a little over $300, but the hell.  I needs my fix.  These all hit most of the points I wanted: All of them run on the flatter side (Heirs and Westones more so), not bass heavy, with comparably better treble than most IEMs I read about on here.  I hadn't really considered the Westones before since I wasn't thinking about buying used, until I saw the 4.ais and drooled all down the front of my shirt.
 
Aaaand fire.

 

[hatefulsandwich]

I remember reading about the possibility of having your 1.2 version upgraded to version 2, so that might also be a consideration for the future.

 

[ocharlas]

paypal sent, (semi) done deal.

 

[Deadlovestory]

Quote:

paypal sent, (semi) done deal.

So what did you end up getting?

 

[ocharlas]

4.ai

...as if I ever really had a choice

 

[ocharlas]

Just thought I'd update this with the resolution:
 
4.ai's arrived today in perfect shape (thanks DRaven5494) with all proper accessories and even a couple extra tips.  These things sound fantastic, and are exactly what I've been looking for - Neutral, beautiful treble extension, detailed detailed detailed, and nice tight accurate bass.  
 
Also thanks deadlovestory for vouching for Heir, and even sending me some more info them.  Hearing these now I realize that I wouldn't have been satisfied with my first choice, the UM3x.  Now if you'll excuse me, I have to shuffle tips around for the next couple hours.