I'm looking for some over-ear headphones up to $1k but lower is better either closed/open (will be used mainly at home not for on the go) and mainly to listen to Vocal Trance/Alternative Rock/Classical. Currently I have a Grant Fidelity TubeDAC11 that can drive headphones down to 16 ohms. Thanks...

Yes

The DAC acts as an external sound card.

Sometimes the sound just stops working and I have to go into the Console and switch to a different speaker configuration to get it to work again. I got one of the first ones so it could possibly be hardware but I contacted Auzentech and they said it's not there problem and would not let me RMA...

I was hoping to get rid of my Prelude which does have S/PDIF output. The driver issue I've had with it has never been resolved and I'm just wanting to get into better audio equipment.

I currently have an Auzentech Prelude as my sound card but am wanting an external USB DAC and was wondering what is the best option for ~$500 to pair with M-Audio A40 and also has headphone amp. What are good headphones to get also to listen to vocal trance mainly?