I took the advice and made the 30-mile trek to GC today. And thank God I did. I was all but sold on the HD-25 II -- to the point where I debated just ordering them on Amazon, but figured I'd grab them locally because I'm getting antsy.
Long story short, I'm back home now two hours later empty-handed. Upon arriving and asking to try out the HD-25 and SRH-840, the guy unboxed each and handed them to me, then gave me a blank stare. I asked if there was any quality stereo or amplifier I could hook these up to, to which he responded: "uhh... you don't have an iPod or anything?" And so my cheap-ass smartphone was my "source" for this listening test. Hooray.
I tried the HD-25 first, and found the bass overwhelming. In addition, as I suspected, the comfort factor was firmly in the negative category. I didn't really hear the bright/trebly sound their reputation suggests, either. Next up was the SRH-840, which sounded similar, but with less bass (a good thing). The salesguy convinced me to try the Beyer 770 (80 ohm) as well. They were by far the most comfortable of the trio and seemed to leak the least as well, and honestly sounded less bass-heavy than the HD-25, despite their reputation. However, they would not get reasonably loud, even with my phone's volume on 10. Clearly, an amp would be a requirement with those.
Now I'm left confused and generally down on closed-back cans. I get the feeling I'm just not going to be happy with the sound from any of them, to be honest. I own a cheap pair of Senn HD497's I bought for $50 back in the day, and I think I prefer them over all three models I tried today. (And this coming from someone who prefers aggressive, forward, bright equipment -- the opposite of the Senn sound! Perhaps closed cans just aren't capable of such a thing?) The only complicating factors are (a) the lack of amplification in-store today, and (b) the possibility that break-in would tilt things significantly.
As much as I want a closed-back set that doesn't leak, I'm awfully close to just ordering the SR 80i and being done with it. If it's going to save me $100+, the need for an amp, *and* have a sound more suited to me, why not? I only wish I knew exactly how bad the leakage is. If it's no worse than the HD497's I've got, I could definitely live with that.