I see a lot of DAC and headphone amps on the site, and I'm wondering why I would need one (or both?). I listen sometimes on my computer, sometimes on an iPad or iPhone, and sometimes on an old school stereo with a Sony receiver. All of these are compatible with headphones, so what's the purpose of getting a DAC/Headphone amp? And what is the difference? And do I need both?
Thanks in advance for any light you can shed on this for me.