It might seem like a trivial thing to do, take a digital stream and convert it to an analogue signal suitable for amplification. But it's not. Digital-Audio Converters (DACs) are hight-precision pieces of kit that are designed to provide the best quality signal to your amplifier. You enter a world of microsecond timing errors, jitter, interpolation, clocking and reclocking, over-sampling. All of it affects the sound. A low quality DAC will pull your entire audio system down: you simply won't enjoy the music so much.
On the other hand, a high-end DAC will make more difference across the board than any other component in your hifi. If you want a large loud choir to sound like a group of individuals singing rather than a smeared noise, then you only have a chance if your DAC is half-way decent. If you want to hear loud distorted guitar sounding like it actually sounded in the recording studio rather than with a sheen of additional blurring to the sound then use a decent DAC.
Over the years, I've ended up with a heap of DACs of varying quality. My main system has a very good one (the Audio-gd DAC-19): there's almost certainly better out there but sadly there are limits to how much I can spend. See the DAC page for more info.