Wow 100% that sure is loud for me even with a 250ohm headphone. Don't worry too much about amp first. They will still run fine without one with the bad effect that I have written for HD668B in my previous post. With a proper amplifier/ desktop amp they are not just only bringing a bit of potential, they might actually bring out their full potential depending on the match between the amp and the headphone. Try to avoid portable or battery power amp instead. If you do I find the minimum standard will be JDSLabs CMOY BB stock configuration for a high ohm headphone.

Try not to listen too loud especially from a headphone out from your pc. You might damage your ear instead. I've been living for about a year +- without a proper/ using portable, battery power amp for my 250ohm headphone and I find it to damage a bit of my hearing already. Try to listen softer and only blast them after you get an amplifier. I hope here you can find a bit information about the amplification. There are some information might have mistakes because it is too hard to find a proper and correct information in an audiophile world. Too much misconception that I'm trying to correct. Here's the link http://audioreviews-akuma.blogspot.com/201...-headphone.html

Basically headphone amp is unlike most speaker amp/ budget speaker amp, their main purpose is not to increase the volume though increased volume is one of the side effect you get from proper amplification. They are meant for improving the controls on the drivers/speaker instead thus increasing the amount of details, bass punch and certain matching can increase the speed/PRAT as well. In other words, headphone amp helps you reduce the your listening volume instead because you are hearing more details than not having a proper amplifier.

Sorry for bringing this old post from previous thread. But I think this is something that is important and should take note of.