I have one of the first NFB-12's that were shipped, i.e. before any of the tweaks or additions of filters. It has served me well and continues to perform dutifully with my Ultrasones Pro 900's. I'm curious what's the next step up, in terms of performance and quality. Since I have been so satisfied with my combo for the last couple years, I feel like I've fallen behind on what's all out there, and what's a good deal vs what's not. I'm also unsure if it would be wise to look for a separate DAC and amp--and if that's the route, which brands can I trust? Most of my music is some type of electronic/edm, but I have a sweet spot for jaz and contemporary instrumentals. The only headphones I use now are the Pro900's and some M50's, but I plan on branching out a little more as I continue to play 'catch up.' I have like what I've heard of DT880's, and have also been recommended HD650's. Any suggestions that would make any of these phones sound better than the stock headphone jack would be immensely appreciated, since I have no idea where to start looking. If it helps, I would consider researching anything below a $400 pricetag.