It is possible, although not very beneficial unless using a much better spec'ed DAC. Marantz has an inbuilt DAC so you could connect your laptop via USB directly to your amp.
Yes you may use the Dragonfly USB DAC to connect your computer to any amp with a phono or 3.5mm inputs.
However this is not recommended as the Dragonfly has a headphone amplifier built in to it and in my experience this do not make a good sources for stereo amplifiers. However, this is a rule of thumb and not a hard fact.