When we designed Saffire, our intention was to provide a throughly professional audio interface at the most accessible price point possible.
A decision was made that the headphone drivers should never, under any circumstances, clip internally. We felt that accurate monitoring was a mandatory requirement for such a product. In any analogue circuit there is a maximum headroom, and our circuit is optimised to meet this headroom at full scale, but never exceed it.
As a result, whilst Saffire is louder than most soundcards (indeed louder than Mbox, which we designed for Digidesign), it is certainly true that by overdriving the headphone circuitry we could have achieved higher level. We chose not to, to ensure that you never suffer the effects of clipping whilst monitoring, since this is almost inevitably counterproductive to any critical listening. The output drivers on Saffire are optimised so that any headphone impedance will not present an issue, although it is true to say that higher impedance headphones have a tendency to output lower levels. We can confirm that the figures we publish relating to flatness of frequency response, THD+N and output levels are correct.
We have, as a company always taken great pride in delivering the most accurate signal paths available. The Saffire headphone drivers deliver an accurate, nonclipped monitoring signal.
If high output levels are required, then a headphone amplifier with either a larger headroom, or the capacity to overdrive the output will resolve your issue. As stated above, we chose not to provide this functionality within the box, quite simply so that it was impossible to get a distorted signal through unfortunate configuration of settings.
We're sorry if this design decision has presented an issue, but hope that for your recording work, it continues to be the product that we intended it to be.