As an aside, I do tend to purposely use subpar recordings to subjectively test headphones. There is a good reason for this which I will explain in a bit. This of course comes down to the matter of what is neutral frequency response. There has been a lot of misunderstanding of neutral. One such misunderstanding has been the straw-man (falsely assumed of neutrality proponents) argument from none other than Steve Guttenberg that neutral frequency response is an attempt to get closer to the artists' vision. (When I play bass guitar or piano, I could give a rats ass about how it sounds on the HiFi - it's the performance that matters.) Neutral frequency response is very simple. It's simply a reference, albeit difficult to exactly define subjectively with 100% accuracy, which one tries to shoot for. Subjective observations of neutrality will vary slightly from audiophile to audiophile. Subjective observations of what is neutral vary little among recording engineers. (UE was not kidding, making stuff up, or futzing around when they said their reference monitors were tuned by sound engineers at Capitol Records.) Even though the "neutral" bullseye may be fuzzy subjectively, at least we know there are people who try to shoot for it. Because of personal tastes of sound engineers (or even directives from Studio Execs), we will see variances in how material is mixed and mastered in terms of tonal response. For example, the guy (don't remember his name) who does a lot of the Patricia Barber stuff prefers a darker sound (with close mic'ing) vs. the guy who did the Bowie Let's Dance remaster a few years ago. Natalie Merchant's Tigerlily is dark compared to the MFSL Pixies stuff. So there's always going to be variance. What I love about "neutral" is that this variance will almost always sound acceptable on a neutral system. I like to use MFSL Nirvana Lithium to test upper midrange issues. A few tracks from Radiohead The Bends I also like to use for this test. The K550, at least the "defective" pairs which I've heard, massively failed this test. You can call it shitty music or whatever; but the fact is, I feel the interpretations are spot on from the recording engineers for these two discs. Certain performances are supposed to sound aggressive. But on bad system or system with upper midrange issues, this is going to sound nasty. I like to use Natalie Merchant's Tigerlily to make sure systems are not too dark. Systems which are too dark tend to suck the life out of that record. I also use Talking Heads Naive Melody (remaster) to test for a variety of many things (too much bass, vocal sibilance, percussion nasties, etc.) What I don't use is classical music. Classical music is generally bandwidth limited.* Now comes the question: is a transducer which sounds good on classical / girl+guitar / flamenco guitar, but not with modern popular music a good transducer? IMO, the answer is an unequivocal no. I'm not into mid-fi. What it comes down to is that a neutral system will be the most flexible with the most recordings for most (but not all) people. Does this invalidate personal preferences? The answer is also an unequivocal no. Heck, I happen to think the HD800 works really swell with Tigerlily. The HD800 really helps liven up that recording. Although I'm sure others may prefer Tigerlily from the LCD2 instead. BTW, I do prefer a very slightly dark sound. The Paradox s/n 001 fits the bill. So did my modified Jades. The UERM is slightly too "reference monitor" for me (it's based on the Yamaha NS10 studio monitor), but I do like the UERM. As of 2015, I am using modified Sennheiser HD650s. Finally, as along as a transducer has smooth response, I'm generally OK with it and can adapter. So even then, I wouldn't say that neutrality is my number one priority (another misunderstanding which folks have attributed to me.) Number one priority is a smooth response (no peaks). EQ'ing a screwy frequency response is difficult. EQ'ing a smooth response is easy.