The ATH-AD700's have plenty of bass 'capacity'. I first listened to them via motherboard onboard sound (nforce4 drivers) and it is terrible... you get a lot of low-level static interference coming out of the source. This has nothing to do with headphones, it is the motherboard/drivers. But because the headphones are so much better than the source, you can really pick out the flaws in the onboard sound. I'll be replacing this soon I hope
Then I plugged them into an old Luxman L-114 amplifier (produced ~1981-1983!), turned on the "loudness" toggle (extra bass) and they were performing perfectly. It was also amusing that this 25 year old amplifier was outdoing modern day integrated sound cards.
I felt that the extra bass toggle (a light EQ) was required, but again it depends on the source being used. Classical/jazz/etc can probably get away without any EQ'n/bass boosting. But without EQ'n, you can start to lose the bass guitar in rock music. But there are so many factors like music genre, the song, the source you use, volume you listen at, personal preference, etc.
For a bit of fun I wanted to see how deep they'd go... and it was impressive. I cranked up the bass control on the amp to maximum (no/little distortion!) and you can feel air being pushed into your ears (and out the back of the headphones). So the ATH-AD700's can certainly pump out a lot of bass if you are into that sort of thing (I'm not a bass-head).
They are very comfortable, as long as you have your head looking straight all the time. Because they're so large, you can't just move your head to look left or right - the headphones will get in the way. This isn't a huge issue to worry about for most people (as you aren't likely to rotate your head 90 degrees all the time while using these headphones). And the comfort certainly makes up for this.