Just wanted to update: I purchased the 598's and a zalman clip-on mic. I'll be comparing them with the AD900 when I find someone who has a pair in Arizona, and go from there. Thanks all for the input and insight. If anyone knows of some amazing microphone, don't hesitate to inform me on that...

Thank you for all the insight into these headphones and others I haven't heard of. I'm comparing all of these and learning a ton.   I'm starting to favor the 598's, and I'm not to sure why... The AD900's are standing out as well, and now I've got totally new options that you all have...