Hey guys! I know this question comes up a lot on this forum, but from my very limited knowledge of amps and DACs some work for certain headphones more than others making this a pretty reasonable question. So I have an Alessandro MS1i and a Sennheiser HD598 that I've been listening to out of my headphone out on my iMac and now I think I'm ready to take it to the next level My budget is around $500, but I'm willing to max out at $700 if there's something really worth getting, or maybe save some money if there's something cheap worth getting. So far I've seen options such as Audio GD NFB-12 (Seems nice at about$200) Schiit Bifrost + Schiit Asgard (A little over $500 but might be worth it) Fiio E7 + E9 (Most common recommendation in Headphones Section, maybe good?) I have an iBasso D-Zero portable so the E7 is not a necessity to take into account. Also 2 things to keep in mind: 1) I plan on getting an HD650 as my next upgrade (followed by an RS1i if I ever have the money), if this affects the choice. 2) I have no idea what the difference is with tube to solid state, and I've seen some people mention "tube rolling" which to my understanding is rotating tubes out meaning they can break from too much use? (Sorry for noobish off-topic question) Thanks for the input guys!