Well, went to the local shop today and got to try a bunch of headphones. Spent a couple hours listening to the HD598, HD600, HD650, HD800, AKG 701, Shure SRH1440, and the Denon AH-D2000.
After writing my initial post, I ended up snagging the HD600 new from Amazon or $300. Couldn't resist the price. After listening to it for a while today, I'm super happy with the purchase. I'm a big jazz fan and they sounded amazing with jazz. I couldn't decide which I liked more between them and the hd650. The 650 has some more bass which I really like.
Speaking of that, I loved the sound signature of the Denons. They only had the display AH-D2000 and they wouldn't sell it to me! So my buddy found a pair online that I'm gonna meet up with the guy and try to get. He's asking $200 for them. Hopefully, I can add that to the collection this week.
My favorites though were the HD800 to no surprise. That's still a long ways off for me.
From what I've read it seems like the HiFiMan HE-400 fits my taste. I'm gonna flip my ATH-M50 in Seoul as I don't use them any more they have nice resale here in Korea and sell my yet to be purchased Denon's later in the year perhaps in the States. Headphones are generally way more expensive here in Korea but there are some nice opportunities to buy in each country and sell in the other.