DAC is an abbreviation for digital analog converter. it converts the data from your audio source to analog power signal
and amp takes that signal and ramps it up so it has enough current to driver your speakers or headphones
Sure thing. To sum it up, the dac converts the digital signal to an analog signal that is sent to an amp to make usable for a headphone. Your pc or phone will have a dac and an amp in there, but it’s not to the quality level of the ones mentioned here. The 1990 is a bit harder to drive (but not that hard) and appreciates a higher quality amp and source signal to sound good
Ok thank you both a lot this helped me tons. So my choice is gonna be the 1990 with that d10 dac and atom amp. And thank you for explaining that to me!
Sure thing, if you have any questions just ask 
So with the dac/amp I will have to connect the dac to my computer, and connect the dac to the amp, and power both of those separately. And also plug my headphones into the amp.
Also what does DSD and PCM mean?
So PCM is Pulse Code Modulation and it’s a form of creating digital audio to sum it up. Almost everything digital you hear is PCM. DSD (Direct Stream Digital) is a bit different and is a standard pioneered by Sony with their SACD (Super Audio CD) for higher quality sound. Limited music is available in this crazy high rez format, but it is nice to have if you need it