Depends what kind of music you listen to for sure, the k702's have almost no base response and are extremely flat. while the 267's are more "fun" and bass heavy
You should be able to find a laptop with a 970m for around 1000 usd, then id suggest thhat if you can. If not then 960m laptop will do fine. Maybe get a 970 for your desktop once pascal drops the 900 series prices
I believe there definitely should be an option to disable this, although i dont see why there would be a problem with using both. the system will take advantage of the discrete gpu if needed