Really interesting question. I'll start by acknowledging the mahogany TH-X00's cost ~8X what the Marantz MPH did ($399 for Massdrop TH-X00's vs ~$50 for MPH-2's). That seems to imply an unfair comparison. But reality isn't that simple or linear (bear in mind I haven't heard the TH-X00's since I sold them last August):
TH-X00's:
- Build/appearance: Pretty--as of May, 2016, the best I'd seen in headphones, with pretty mahogany cups, nice headband, above average earpads
- Fit/comfort: Well above average w/relatively light clamping pressure, no big hotspots, etc. I'm reasonably sure the angled earpads were leather or lambskin vs pleather. I had a little trouble getting a good seal, but then I usually do w/angled pads.
- SOUND:
- The bass really got my attention. I'd never heard sub-bass, and these headphones have that. The rest of the bass was quite good (deep/impactful), but subtle qualities like sound of strings (stand-up bass, electric, etc), "roundness" of bass notes, etc, weren't quite as good as the only other headphones I had then, the Fidelio X2's. The bass also went down slightly in level as it got into the midrange.
- The midrange seemed recessed to me (I was still learning headphones then), but not bad overall.
- Upper midrange: trouble here, with a peaky quality setting in.
- Treble: real trouble for me here w/elevated, bright treble. Notes also didn't separate well...some grain/roughness in the treble. Things like massed violins in classical music didn't sound they way they should IMO. Lots of detail, but not great clarity or listenability
- Dynamics: plenty of dynamics, but in the peaky upper midrange & treble, that actually made the tonal issues seem worse
- Soundstaging: average at best. With wooden cups, I expected a more spacious rendering of music, but that's not what these headphones do
Net/Net: I found the TH-X00's to be a rather neutral, dynamic, exciting HP. But it lacked any quality of warmth or roundness of notes in bass & lower midrange; and was just too bright/aggressive for me.
Marantz MPH-2's:
- Build/appearance: Not in the same league as the TH-X00's, of course--lots of plastic & pleather. But I find the Marantz, with its gold-on-black color scheme, to be rather handsome (and better than the other ISK MDH9000 clone I owned, the LyxPro HAS-30)
- Fit/comfort: Above average. The clamping pressure is slightly more than I like, but not enough to be aggravating. They're relatively light/easy on the head. No hotspots. The earpads are (for me at least) very comfortable--relatively soft and plenty deep. Easy to get a good seal.
- SOUND:
- The bass is excellent & enjoyable. Less sub-bass here than the TH-X00's, but the rest of the bass range (where the music is) instantly satisfies. Bass is deep & impactful, but also has a subtle quality of "roundness" and air in the notes, which billow, then tail off as they do IRL.There'as been discussion here whether the bass is elevated or not. I find it to be moderately shelved up, but not in way that intrudes, and w/o any peaks/bumps. To me, the bass is very pleasing & accurate.
- The midrange seems just about right to me, not recessed or hyped. There plenty of detail and a pleasaing sound quality in the midrange
- Upper midrange: again, just about right--detailed yet pleasing. Voices sound like voices.
- Treble: I've heard all kinds of music on the MPH-2's and the treble always satisfies. It's level, un-hyped, with plenty of natural-sounding detail
- Dynamics: not at all lacking, but also not dramatic & noteworthy. Music flows in a natural way IMO.
- Soundstaging: certainly better than I expected for the price--also better than the TH-X00's. Like everything else w/this design, the soundstaging is above average and sounds "right."
Net/Net: IMO this is a real over-achiever design that sounds way better than anyone could expect, given its price. Everytime I use the MPH-2's, it's the same thing: I quickly forget they're on my head and just hear music. I've owned 3 examples of this design; they all sound exactly the same. From day-1 I felt these could be used for professional monitoring use because of their overall balanced, yet listenable sound.
I recently found the MPH-2's to demonstrate another positive quality: they scale way up when fed signal from big-time/powerful amps. I have 2 amps w/what I regard as very distinctive/interesting sound signatures, though in totally different ways (Audio GD SA-31SE; and Violectric V281). Using each w/the MPH-2's, they sounded even better than usual and clearly conveyed the distinctive spatial/tonal qualities of each amp. This impresses me to no end...one could hardly expect $50 closed-back headphones to scale up & match amps like this--but they do.
(in fairness, that's a test I couldn't perform w/the TH-X00's, as I didn't own these amps then).
BTW, the only Fostex design that currently interests me is the E-MU Teak (based on the same frame as the TH-X00's), based on it's reportedly epic bass capabilities and smooth, pleasing overall sound.