Xonar Essence cards will drive the K702's with ease to loud volume level. It's only at high volumes the K702 and it's cousins are harder to drive than a lot of other low impedance headphones.
They can be used fine with a sound card that doesn't have a headphone amp, such as a Xonar DX, as long as the user doesn't expect to be able to turn the volume up loud. Beyond a certain point, something with a more powerful headphone output would be needed, such as an Essence.
It has normal, high and extra high gain options when headphones are connected. I’ll check what the + db for each says in a bit.
Wouldn’t high / extra high gain produce lower audio quality which sort of negates buying high quality heaphones that are harder to drive (unless you spend maybe £500+ on a headphone amp too)
Set the gain to whatever suits you, although it's best to choose a gain setting that allows greater movement on the master volume control; so if 100% volume on lowest gain setting is way louder than you'll ever need, leave it on the lowest gain. There is no advantage at all to choosing higher gain then having to considerably lower the volume.
Regarding whether increasing gain would result in a loss of sound quality; it doesn't produce lower sound quality, it would really be distortion by added noise that is heard. Increasing gain increases the amplification. If there is noise present and you increase amplification, it will also amplify that noise.
Unless you have some interference being picked up by the card or the audio source being played is of poor low sound quality, then you shouldn't have any issues even on high gain setting.
I have a Xonar D2X and an O2 Amp, I am hoping they will suffice.
As with the Xonar Essence; O2 amp will have no trouble driving the K702's to a very loud volume.
How does the vmoda boom mic connect the 702s? ...As the 702 do not have 3.5mm male connection
You'd need a mini XLR to 3.5mm adaptor. They aren't overly common, but they do exist. They do add bulk and distance from headphone to microphone. Some people are OK with that, but it's certainly not the ideal microphone to use with the K702 and similar variants.
