Reason for this comparison is because these three are the most comfortable headphones I've ever used. They are also in my favourites list.
I'm going to just jump straight into this.
All three are amazing, the MA900 has what I'd all a floating design, the ear cups don't clamp me at all and the pads are very unique. The frame is also so light and minimal that it's the perfect long term headphone and also suitable for summer. The Mad Dogs are a lot heavier with a tank like design so you will not get the same comfort as the MA900 but for the time you do wear them they are very comfortable.
The ear pads are huge similar to having pillows on your head. They do get a bit sweaty as your ear is quite congested in there and it isn't that breathable after around an hours use but the Alpha Pads really are an excellent pad. The comfort strap is also a good little idea as it takes any pressure off your head so you don't have to deal with that horrible head band.
The D600 are also nice on the head. The lush memory foam pillows make your experience very nice, I would say these are the best pad on any headphone. it's soft, quite breathable and shaped like your ear. It's not real leather but it's just as good quality. The headband is quite thin so it's not as amazing as it could be but it does the job and doesn't;t bother you. They are not too heavy I find considering the size. I find I can listen to these longer than the Mad Dog but not quite as long as the MA900 with I can wear all day.
Right away you can see the build on the Denon and Mad Dog is very good. The MA900 however I wouldn't want it to take even the slightest punishment due to it's light, frail build. The Mad Dog is a plastic heavy weight and built like one too. Very few moving parts and could probably take a thrashing especially that headband! The steel rods are also excellent!
The cup design however, doesn't seem as solid as the rest of the phone. Still I would say for a £100 headphone they certain exceed their price point and with the Mad Dog mods it also is up to par. The MA900 is built like a twig...Ok it's not that bad but it feels like it is. If you are careful and use this as a home headphone purely and don't slug it into you nag it will probably survive it's lifespan. The Cable will probably fail at least once so a bit of recalling should be on the cards IMO.
The D600 is Build very well too, It's a Matte plastic design that is very solid with few moving parts. The way it's put together gives the impression of a life long phone, however at the cups I have had one of my pairs come loose inside the cup. It didn't affect anything I simply pressed it back down and it was all good again.
Now in here I am not going to talk about technical terms as I'm not an audio but I understand sound very well and have been doing this for 10 years.
Firstly The M900, It has a very laid back, mellow sort of sound, There is nothing offensive in the sound at all. It's Treble is a tiny bit sparkly but not too much, you could say it's actually quite weak and unremarkable. The Mids are the star of the show with these babies, it has a lush, liquid kind of sound. it's warm and quite seductive. The mid range has nice detail and very natural sounding. Probably the best midrange I have heard under £300 that isn't the Mad Dog...Ooops ;)
The Bass is very good, there seems to be a slight boost but not a lot at all. I would even say it's how it should be IMO but it's a subjected thing really. It's not really a full kind of Bass but it is there and when called for it can have a bit of oomph to it at times. Another star in it's arsenal is the soundstage, this is a true soundstage headphone. I have owned many open backs, K702, DT880 etc and this is superior in soundstage. it's not just wide it's deep and has a real atmosphere to it. it's airy and spectacular! best soundstage I've heard period, The imaging is very good too; probably close to perfect.
The Mad Dog, It's sound I would describe is similar to the MA900 in a warm, it's warm, lush and liquid. The highs again are unremarkable, a tad boring sounding. Mids are really nice on these, it sounds FULL very thick sounding Mids and juicy. I would say if you've heard the MA900, in the Mids they are excellent but not really thick or full, The mad dog sound beefy in comparison. The Mad dogs Mids I would say are probably the best I've heard yet overall.
The Bass on the Dogs is full sounding, it doesn't have the most impact but it's pretty powerful. It's not a Bass heads bass but the quality is outstanding! no complaints. The soundstage is pretty good considering how sealed this phone is. the Alpha Pads I imagine help these out a lot. it's on par with phones like the DT770, HD650, LCD 2 in soundstage! The imaging is very good.
The D600 are a lively and musical headphone. The Treble is Sparkly and detailed, it sounds how I expected from Denon! at high volumes it can be a tad strident on some songs but it isn't too bad. I find it a good high and it's superior to the other two.
Mids on these are excellent quality, they sound similar to the MA900 is quality, thickness and warmth. The D600 Mids however are a little drawn in, they are not recessed but are less forward. They are musical, detailed and won't disappoint. The bass on these babies is fooking awesome, it's lively, full and just big!! Best Bass I've heard out of the three! although the Mad Dog is close in enjoyment.
The stage on these is big too, larger than the Mad Dog, DT770 and not too far from the K702 but no where near as airy as the open phone! the imaging is good too although the Bass is very strong so it doesn't affect it.
Mad Dog> D600>MA900
Now my rating is basically what I enjoy more, for example, the MA900 has more forward, lusher mids than the D600..but I find the D600 to have slightly better quality and excitement. These are all excellent and all are a bargain at their price. my overall fav goes like this
I just enjoy them more! More musical, although less accurate in comparison they are not far behind at all in that regard considering they are a bit coloured. You can't beat a headphone that draws you into the music and makes you forget about the price you paid and more on how much your music is alive!!
Cheaper, better value considering the gap at Mid Fi is small these are priced at Entry but are comparable to high end Midfi like the HD600!
If the Denon where £400 instead of £200...sod it I'd still get them! best headphone I've owned simply because I just love mythe way my music has personality.