£200 better is coming into the territory of diminishing returns and it's hard to quantify in those terms like 10% better etc. as there are so many factors which make up a sound signiature.
You have to consider that users will have some form of confirmation bias based on what they own so take that into consideration when you hear claims of 'best headphone at a price point'. Everything comes into play, what one's reference point is, preferences, sources, music choice etc. There is no 'best headphone'; one man's nectar is another's poison. I am primarily a collector and everything I own has a weakness of some sort or another as well as strengths irrispective of budget. Saying that there is a best headphone is like claiming to know what the best food is.
I know I've heard the MDR-100AAP, at HMV where there were a bunch of headphones on display, but they left little impression on me because I recall them sounding soft; we're talking a 10min audition a while back but soundstage was decently wide, they sounded clear but with an obvious treble roll-off and recessed mids which left them lacking attack but also punch. Purely on performance, at their price point they're not at the top within their budget whereas a headphone like the Meze 99 is at the top at it's price point.
The Meze 99 has a similar soundstage, a sweeter more forward mid range, more extension in the treble and a slight boost in the mid-bass which provides a sweeter presentation for vocals. They are extremely capable, easy to drive and provided you can get used to the clamping (which softens over time anyway) are fairly comfortable. Can't comment on the larger pads because they weren't available when I looked at them.
When looking for a replacement to the V-Moda M100 the 99s left the M100 sounding like it lacked resolution; a clearer more detailed presentation. The M100s have more mid bass as well as reaching deeper but the mids/vocal presentation on the 99s is sweeter, more upfront and more emotional. The treble is similar on both, to my ears but due to that clearer presentation, the 99s make it easier to discern detail and are more resolving. The bass presentation has far more emphasis at around 150-200Hz though and there is roll-off below which means I couldn't hear proper extension into sub-bass regions which is something I personally hold as quite important.
They are a very musical headphone with a warm, fun, inviting tone.
Now... the following is more for clarity around the Audeze Sine and for the most part you can ignore what is in italics as I'm not going to recommend them anyway:
As for the Audeze Sine, I can understand again that preference will come into play but personally I do not like the implementation of the Lightning Cable compared to a decent source despite what other professional reviewers state. The Sine headphones capabilities excel what the Lightning/Cipher cable can deliver and in that respect scale suitably with better sources.
In comparison, the Audeze Sine makes my M100s sound like pure mud. The Sines are not bass neutral, it is, however flatter than the Meze. I understand some have a preference for more mid-bass emphasis however the Sine has a noticeably deeper bass extension with the ability to convey serious bass texture and for the most part, is what I listen to metal and electronica with outside. Presentation is clear and visceral. The bass is tight and nuanced to the point where they present instruments like kick drums with a noticable impact. Mids and vocals are wonderfully balanced and treble is well extended though I do note a dip at around 7KHz... a frequency I am not a fan of anyway. It means you can turn up the volume without experiencing issues on simblant tracks. The resolving capabilities are their most impressive aspect by some considerable margin. The amount of texture they can convey is astounding given their price and for me are the one mid-fi headphone where I don't feel I'm compromising as much compared to what my desktop headphones deliver while I'm out.
Their sound signiature is more of a warm reference sound while still retaining a musical presentation.
So I had the Meze 99 and Audeze Sine at the same time for about 2 months. Comparing the Meze 99 to the Audeze Sine, the 99s are warmer sounding with more mid-bass emphasis and slightly more warmth in the lower mids. The Sines are more of a warm reference sound with a faster, clearer presentation and deeper bass response to the point where it is quite noticeable that there are sub 80Hz frequencies the 99s simply do not deliver on. Moving into the mids, the Sine has a less sweet mid presentation than the 99s due to that mid-bass boost however vocal presentation is clear with both. Treble presentation on the Sines is more detailed than the 99s however that is not to say the 99s are lacking, it's more their signiature is that much warmer throughout the spectrum. The Sines sound more resolving, due to that clarity, all the way to the top frequencies.
Comfort wise the Audeze Sine also clamps but not as hard as the Meze 99s however the 99s are slightly lighter for long term use. On a personal level I prefer the minimalist black look of the Sines compared to the exotic mix of metal and wood of the Meze which is a little 'inyeface' for my tastes. Ultimately I gave the Meze 99s away as they didn't have a niche to fulfill.
I note Tyll's review PL4Y3R 0N3 linked. Tyll has a preference for a slight 150Hz emphasis, which I think is the preference for a majority of headphone users and partially why he also liked the Meze 99, adding it to the 'Wall of Fame' at their price. Nevertheless I also note that in his review for the Audeze Sine he stated they will go onto the 'Hall of Fame' at the highest point within the closed on-ear category at any price:
http://www.innerfidelity.com/content/sports-car-your-head-audeze-sine-and-cipher-lightning-cable#PTCu1Sx6ZiL1Bf7O.97
All that said my details on the Audeze Sine is now going to be rendered moot as I am going to join everyone else in recommending the Meze 99 for your purposes. The problem with the Sines is they are source dependant... and by that I am talking about power and tonality. My Sines are harder to drive than some of my TOTL headphones, which makes for one problem and the AudioQuest Dragonfly is limited to a 2x45mW output at 32Ohms, given it is powered off a USB supply; simply, it will not drive them properly. Tonally they benefit from a warm, detailed source and the Audioquest Dragonfly is more neutral... or at least the DAC it utilses is... as I'm only familiar with the DAC, not the Dragonfly. Even with expensive sources, a less warm feed will make for an anaemic pairing.
I feel the warmer presentation of the Meze, despite it's lack of sub-bass extension, is going to be more to your liking given what you're looking for. That said I think the budget has to be increased significantly to find a headphone which will out perform it while retaining its strengths. As well as this the Meze are far more forgiving with poor recordings and that is going to be amplified if you're using them to stream compressed media. Lastly they do not require an uber powerful or specifically tuned source to sound their best... though they do benefit from a decent source with brighter tonality. The Audioquest Dragonfly utilises a Sabre ES9010K2M DAC which err on the side of neutral (compared to, for example the warmer presentation of Wolfson DACs) and this should make for a fine pairing.
Given your requirements, preferences and source, there really isn't much competition to the Meze 99 for your purposes.
I wish you luck on your audio journey.
