Recomendations for best studio headphones

BeyerDynamic DT250 or Audio-Technica ATH-M50 (more bassy than the DT250) would fit the bill pretty well IMO.

Sony MDR-CD900ST

I'd say Sony MDR-V6 or Ultrasone 750 (tho I haven't heard these Ultrasones yet, people say they're the only real cans with punchy bass).

Audio-Technica ATH-A900 would fit the bill. A bit tipped up at the frequency extremes but nothing major; certainly nothing like a Beyer DT770. Good bass output, reasonable detail, and a very wide soundstage for a closed can.

For my studio work I went with AKG K271s... since I'm looking at them for monitor and dub usage. I'm not sure if I would say they meet your tons of bass requirement...

The DT770s do not have a balanced response. They sound great and have tons of bass, but I wouldn't recommend them for recording work at all. A friend of mine who does a lot of recording uses the ATH-M50s and is quite pleased with it.

I think my DT770 are very well balanced, except for a slight dip in the lower mids.

^Agreed. DT-770 are studio workhorses. They are only perceived as non-balanced to audiophiles who find bass offensive. Secondly, you're probably better off asking this question in a studio forum.

It's very difficult for me or anyone -I guess- saying which cans are the "best" for any purpose

If you want them to master recordings at home and need isolation, my recommendation would be the Sennheiser HD25-II. They have more bass than all the others, in fact it's a bit enhanced compared to the others, but it's the only which is really capable to have a significative response under 50Hz. Have a look at this graphs comparing the frequency response of the Beyer 250, Senn HD25 and 280, and AKG K271S.



The graphs probably aren't the most accurate thing to consider, but would give you an idea of what to expect from any of them.

Rgrds

Also don't forget that these frequency graphs are done using a 0-ohms output jacks. Beyers, for example, are all designed using 120-ohms output jacks. That might change the response a lot.

A 0 Ohm impedance output jack just means that the device they used to feed the cans with the signal has a very low source impedance. This shouldn't interact with the cans own impedance. It's one of the best possible conditions. It'd be very worse using a 60 Ohm output impedance to drive 32 Ohm cans.

Rgrds

Headphones are not perfectly resistive devices, hence the use of the word "impedance" rather than "resistance". Adding a series resistor changes the frequency response a lot, especially in the bass and lower mid frequencies.

Having that said, I think Beyer headphones sound a lot better from 120-ohms jacks than 0-ohms jacks, regardless of the headphones own' impedance. I guess it's partly because they were designed that way. Thus, the graphs found on Headroom don't reflect the "true" chracteristics of the Beyers, which are what the designers came up with by using 120-ohms jacks.

Why do you say it would be very worse to use a 60 ohms output with a set of 32 ohms cans ? Many argue that damping factor is an issue with speakers because of the much greater diaphargm mass involved, but not with headphonmes. Even then, some of my university professors strongly believed that you should always match the output impedance of your amp to the nominal impedance of your drivers (headphones or speakers) in order to balance the forward and reverse excursion damping factors to give the greatest fidelity. Thinking of it, it makes a lot of sense. People are too used to "dry" bass these days.

A zero ohms jack isn't always the best choice. Also, think about the IEC standard that specifies a 120 ohms output jack. I believe ALL headphone manufacturers should stick with this standard, but as standardisation is optional nobody can oblige them to do so. The adherence to this standard is one of the many things that I like about Beyer, my now favourite headphone company. I wish other companies would say more about how they design their headphones.

OFF TOPIC : BTW, are the Denon D5000/D2000 Made in China or Japan ?

It's just a matter of power transfer. The ideal condition would be that the output had the same impedance as the load -disregarding damping factor considerations-, but provided the headphones may have changing impedances across the frequency range, that's almost impossible, unless you use Grados that measure a commendably flat impedance accross the spectrum.
If you use at the output a higher impedance than the load, then you're "wasting" power which cannot be properly transferred to it. It's a more desirable condition having a lower impedance on the output side than at the load's. The opposite condition, which is what you find using high output amps like tube ones, driving low impedance cans, is more likely to produce roll off at the frequency extremes of the audioband.

I suppose the studio standard of 120 Ohms output is a compromise one which would work on most pro cans having 120 Ohms impedances and higher. Low impedances are mostly found on consumer headphones. I wouldn't like to drive my D5000 or R10 from a device having an impedance of 120 Ohms or higher.

Looking at my D5000's box, it says they're "made in China".

Rgrds