Hi--this is my first-ever post after at least a year of lurking on this forum. But since I happen to own both pairs of headphones, I thought I'd chime in. I got the 225s first, and thought they were a huge improvement over my previous cans (Sony V6), especially in clarity and definition. I was so impressed with the improvement that I decided to finally buy a real CD palyer and headphone amp (NAD 541i and Grado RA-1).
But I could not get the RA-1 to play at a low enough volume for reasonable listening without the balance shifting to one channel. Eventually my dealer replaced the amp with his floor model, which was a little better (but I still can't turn the volume much past 7:30 or so--is this normal?). In the meantime, though, I was curious about the HD600 and figured that as a high impedance can it would be less likely to have the volume problem (which was true--I can maybe turn the volume knob up to 8 o'clock).
Anyway, my first reaction on hearing the HD600 was disappointment--where was the detail? Upon further listening, I noticed that while it did indeed lack some of the 225's detail, it did have a bassier sound and a fuller soundstage, both of which I liked. Returning to the Grados, I would think, "Aha, the detail is back--but where's the bass?" After listening to the 225s, the 600s always seemed to lack detail, but after the 600s, the 225 sounded thin, even "tinny" in comparison. The upshot was that I could never decide which was better for very long, and was getting upgraditis.
Then I ended up making two more incremental improvements that made big positive differences in both sets of cans. The first was getting the Cardas replacement cable for the 600s. I was worried that it would be a subtle difference at best, but that was not the case at all, to my ears. Without even any break-in time, I immediately noticed a huge difference in detail. I am now firmly in the camp that feels that HD600 indeed has a "veiled" sound, but that the Cardas cord does a lot to remove it. In fact, it had almost all the detail of the 225's without losing any of the added bass and soundstage.
I had given up on the 225s entirely before reading about the different pad modifications. I tried reversing the bowls and thought it may have added some more bass, but not enough to really rival the 600s. A few months later, however, after seriously upgrading my source (but not the amp), I tried the reverse bowls on the 225s again while listening to a CD that sounds unusually murky and lifeless on the 600s (Seal's HUMAN BEINGS). And voila, not only did the extra impact of the 225s make a huge (and expected) difference, but I noticed something new about them--with the bowls reversed, they no longer had that somewhat shrill sound, but had a particularly lush midrange, particularly with vocals, guitar, piano, and wind instruments. In fact, the midrange had a "glowing" quality--perhaps it's what people refer to as "lush"?-- that just isn't there with the Senns (and that doesn't really come through with the bowls, either).
Now, I tend to use the 225s most of the time, but interestingly, the Senns with Cardas cable and the Grados with reversed bowls sound surprisingly similar, the main differences being in impact and spatial perception. I still sometimes prefer the Senns for certain modern remasters that have overemphasized treble, in which case the Grado impact can be a detriment.
Overall, I would only recommend the Senns if you were interested in their darker, more spacious sound, which actually works just fine for many rock recordings--and even then, I would strongly recommend the aftermarket cable, which makes them much less of a bargain. An interesting alternative, for what it's worth, might be the Beyer 990s,which get very little attention around here. While I don't own them, I've heard them often at a friend's, and frequently consider getting them. They have a very dark sound, with MUCH more bass than even the 600s, which sound almost anemic in comparison--on the other hand, they're even less detailed than the 600s (but not horribly so). This is almost certainly a very 'colored' presentaion, but one which can be aural nirvana for lush recordings like Bryan Ferry's, or for female vocals (the "lush" effect is not hurt by their extraordinarily soft circumaural pads, either). They don't work as well (IMHO) for more "technical" recordings, like instrumental jazz. But they're even more of an "alternative" to the Grado sound than the Senns and tend to be much less expensive, especially as they don't need an aftermarket cable.
Anyway, I've gone on far too long. I wish you the best of luck in making your decision, and hope my saga so far has been of some assistance.
Take care,
Mark
