Looking to upgrade from my Astro A50's to something a bit better. Suggestions?

the 770/990 would be in the "bassy" classification of headphones. that is somewhere between neutral and bass cannon. a good level of bass output without getting muddy or without having poor mids and treble. both are v-shaped with peaked treble and bass with recessed mids. the 770 is more bassy than the 990 with the dt770-80 being the bassiest of the lineup.

what pairs best depends on what you buy. for the 770-80 the soundblaster z would work, the fiio a3 would work and most mid-power products like the e10k, audioengine d1 and similar will also work. for the 770-250 or dt990-250 i would suggest at least the e12 or preferably the schiit magni 2. the o2 amp is also a good product. the e12 has a slight issue with noise while charging so while it works its not perfect. the rest dont have that issue. be aware those are amplifiers not dacs. dac is different. a good dac+amp pairing is the schiit magni/modi stack or the o2+odac. of course if you have good onboard audio on your pc you could use your pc (or soundcard) as the dac portion instead.

as far as what works best for you? that depends on which headphone you end up picking and what features/needs you have.