Yes, you can plug them into the headphone output of an amp or receiver. However, they are quite sensitive so you may be aware of some background noise. Equally, they are of nominally 9 ohm impedance, and as amps' headphone outputs tend to be just a 2-300 ohm resistor in series with the headphones and connected to the loudspeaker outputs, that will form a large potential divider that will reduce any background noise, so noise may not be any worse than other headphones.
As to a DAC, that will take a digital input from a source like a CD player, computer or streamer, and drive the headphones. You need to make sure that any DAC you choose is capable of driving 9 ohms.
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