Headphone output, deciphering jargon

[bishbo2000]

Currently I am using an M-Audio FW410. My setup consists of a Macbook Pro, Slim Phatty, Mono Evolver and a tape delay. I monitor through headphones most of the time (baby in the house).
A problem I have with the FW410 is the level on the headphone output is really low. I use AKGK702 headphones. I always have the output tuned up full when building a track, sometimes I put a Utility in the master channel to +5dB just to maintain a decent level I can use.

I am going to get a new interface. I like the look of the Apogee Duet 2 and the RME Babyface. They should have enough I/O for my setup, nice and compact, and bus powered (I travel a lot, without the hardware)

I don't want another interface with weak headphone output. From their respective websites the headphone output information is given as.....

Apogee Duet 2 : Max output level headphones : 19dBu
RME Babyface : Max output level @ 0 dBFS Phones: +8dBu

and from AKG about the headphones : rated impedance 62 Ohms

I don't know what this means, at first look I would assume the Apogee Duet will be louder, but am I comparing apples with apples? can someone shed some light on this for me please?

Also, does anyone have an opinion on which interface would be best for my setup?

[102455]

It's kinda like the difference between speakers - how can a 100W speaker sound louder than a 200W one?

It's not all about the output level.

Speakers (and headphones) have different sensitivities (efficiency), so with the same amount of signal going in, one may sound louder than the other because it's converting the voltage into sound more efficiently.

Yes the output level of the interface will play a part, and so will the impedance (ohms) of your headphones. Ideally it will be close to the impedance that the output stage was designed to be used with.