I recently got my K702, and I am super happy about them.
The thing is that my audio interface (MR816X, a pretty awesome dac by itself) seems to struggle in powering them. I need to max volume levels to get decent listening volumes, which makes my headphones sound a bit distorted, with some added pressure to the sound. You can really hear it with vocal, which don't seem to translate well with this built in amp.
So I am looking for a semi-budget amp (let's say no more than 300 USD) to power up the K702, with as much as detail possible, and good transparency.