Okay, sorry for the delay...
The 1540 falls more in line with the 440 and 840, rather than the much brighter 940, 1440, and 1840. i've only owned the 840 and 1840, but FWIR about the others I believe my assumptions to be somewhat accurate about the other Shures. I know you tend to prefer brighter headphones, so the 1540 may not be quite in line for you. That's not not a knock on the 1540's treble, it's still extremely detailed... it just doesn't have that spike up top like its predecessors.
The mids are linear... pretty much dead even, though not recessed... but to those who are used to forward mids of AKGs, Mad Dogs, MA900 and the like might find the 1540's vocals to be a bit pushed back.
And then there's the bass. Man, DAT BASS! It's not basshead material, but pretty borderline if you ask me. It's punchy, extends deep, and does not bleed into the mids at all (to my ears, at least). Now, remember, I'm used to forward mids and lean bass myself... so try to believe me when I make that statement.
Oh, soundstage! Not the ideal choice for competitive gaming... but yes, the soundstage is above average for a closed headphone. I've tried quite a few, and it has one of the largest soundstages I've heard in a closed headphone. Definitely larger than the 840, and almost on par with the Soundmagic HP100. I would like to add, though, that the K545 might be THE BEST soundstage I heard in a closed headphone (judging from the one driver that worked).
Disclaimer: These brief impressions are solely based on the 1540 with alpha pads on. While the alcantaras are much more comfortable, the alpha pads refine the 1540's sound signature to the point where I much prefer that over comfort.
Good impressions. Considering the initial praise everyone is giving these and who it's coming from, I think I'm going to try them out. I've also heard of people extending the treble by throwing on the SRH940 pads onto them, so I might try that later down the line.
Personal note: I might be in a slight transition with preferences right now towards something warmer. Surprisingly enough, the HD 600 (a can I originally didn't like for being too warm) has been getting a workout lately. Nothing like my HD 700, but it's definitely not collecting dust how it was before. Those two really compliment each other well. We'll see how that works out. Still, I'm a soundstage and detail retrieval whore.
That being the case and considering your comments, can't wait until you get a working K545.