Ok, my final thoughts on the Shure SRH750 DJ after approximately 60 hours of burn in, which I think is sufficient to evaluate a headphone fairly well. Additional burn in may improve the sound, but from my experience with many headphones, the difference, if any, will most likely be marginal:
With burn in, I find that the treble was tamed nicely and is no longer overemphasized, like it was at the beginning. But as the treble became less pronounced, I also realized that the mids and highs on the SRH750 DJ are really not that great - they are quite neutral, but they lack refinement and especially the upper treble is a bit out of focus, making the SRH750s sound a bit muddy. A good amp and source can make the sound clearer and more refined, but I doubt that the Shures will benefit much from amping since they are so sensitive at only 32 Ohms. The bass quality is awesome on these cans, but unfortunately I find that the low end quantity is simply too much for a lot of music I listen too (mostly instrumental, smooth jazz and pop). It does not drown out the mids and the highs, but the pounding sub bass gives me a headache after a while, unless I listen at very low volumes. Listening at low volumes, however, I find that the mids are also not present enough and not refined enough to allow me to enjoy music.
Overall, I think SRH750 is a solid set of closed cans for the price and beats such other contenders in this category as the ATH-M50, M-Audio Q40 and Roland RH-300 in some ways, it also looses out in other ways. For example, I feel that Roland RH-300 has a better balanced sound, with better presence in the midrange and a softer, more musical treble, while the M-Audio Q40 has a much more musical low mids and better focus. I think SRH440 is also a better choice if you are looking for a balanced sound, even though it may be technically inferior in the bass and treble. The only headphone that I think SRH750 really beat in pretty much every way is ATH-M50, although the M50s may still be preferable to those who like softer mids and highs - the SRH750 presents the upper mids and treble in a rather aggressive manner which some people, including myself don't like. M50 is actually more upfront sounding, but softer due to a dip in the upper mids.
For just a little more, or even the same or lower price, depending on where you buy it from, I think Shure's top of the line SRH840 is a superior headphone in just about every way. The 840s have better clarity, better resolution, more solid imaging and a more expansive soundstage, and a generally more tonally balanced, yet at the same time more musical (IMO of course) presentation. They don't have the glorious, tooth loosening sub bass of the SRH750, but they still provide quality bass response that is still emphasized and warm, but more forgiving at medium to high listening volumes.
Now, it's not exactly a bargain of course, but it's a good price on excellent sounding headphones I think. I auditioned a pair of these recently at Moog Audio (they are currently selling for over $150 there BTW) and the sound is real nice - solid bass, natural mids and good treble extension and quality for closed cans. Also, soundstage is surprisingly vast.
