Preferably yes, at least an amp To begin with. But they do not require a lot of power, typicaly no more than 25 to 30mw (some will disagree, saying that transient power required is over 200 or 300mw.... I don’t agree). They need at least 2v of voltage, preferably more, 6 to 7v at most, for good bass reproduction, but at 330 ohms they require very little current Output. For the DAC, I would say it is preferable to get a good external DAC, because most PCs have cheaply made sound cards with bottom of the line DACs. One exception I would note: if your source is an Apple product, such as a Macbook Pro, or even an iPhone or iPad, these units have better than average DACs from Wolfson or Cirrus Logic (Cirrus Logic now owns Wolfson), depending on models, and are well implemented and you could do with only an external amp using the internal DAC In your Apple unit. This said, if you have the $, it is preferable to get an external DAC and external Amp, or a combo. If you have Apple sources and a limited budget, I would recommend to get an external amp such as the 95$ Objective 2 (O2) or 99$ Magni 3 or a 199$ Aune X7 and get an external DAC later on... or get a combo if you have the funds (O2/OLDAC, O2/SDAC, Magni3/Modi Multibit or not, Aune X1s/X7, Cavalli amps with Grace SDAC, many others also available). If you are on a tiny budget, even the NX1s amp (without a DAC) at 35$ on Massdrop could do it for your HD6xx for a while. Also A very nice but not very powerful DAC/amp is the 199$ portable Dragonfly Red on a usb stick, which carries an very good Sabre 9016 DAC which may eventually be used in DAC mode with a more powerful separate headphone amp. The Dragonfly is not very powerful but generates enough 2.1v of voltage and drives the HD6xx quite nicely when you need a portable solution with a phone or iPad. By the way, the X1s at 199$ currently offered by Massdrop is a nice and cheap DAC/amp combo powerful enough (200mw in 300 ohms) to blow your ears out with the HD6xx. If the Massdrop O2-SDAC at 149$ ever returns, it is probably your best bang for buck to get an integrated DAC and Amp... hope it helps.