Connecting

Slowly the gap between computers and audio is closing but you won’t find many amplifiers with USB input or PC's with a SPDIF out. If you do it is often a multi media model.

Sometimes a headphone out doubles as a Toslink out.

USB DAC’s are becoming popular.

Streaming audio players connect to the audio using conventional connections like RCA or SPDIF (digital).

Maybe you are lucky and you have a connection supported by both the PC and the audio.

You can connect the analogue out (headphone) to your amplifier but the quality of the headphone amp on the PC is often of moderate quality.
Sound card lines out to amp line in or sound card digital out (SPDIF over Toslink or coax) to digital in are the most likely ones.
But most of the time you need to convert.
More details on how to connect the PC to the audio can be found here.