I'm a software engineer and spend 10-12h/day on the computer with the headphones on, Senheisser HD280pro, I know they're a bit bassy, but love them and their noise isolation is awesome (and needed!).
Anyway, I have a high-end motherboard, capable of "HD" audio. HD280 has an impendance of 64Ω, which after days of reading I think it's on the fence of needing or not an amp. For me, they sound great withou one, but a co-worker bought one, try them on and sound goes from great to awesome (monkey see, monkey do).
I've been looking at Fiio E9/10/17 (recommended by some audio store owner), but my main problem is that all of my work is done in Linux, so I'm not sure if a USB DAC will be compatible (the man at the store couldn't answer it). Maybe I should "upgrade" my headphones to something better but I really like them (I tried others from the same price range).
I think I could spent $70-150 on the DAC/AMP, up to $300 on the headphones (if needed too)