HiFiBerry Digi2 Pro is a high-quality S/PDIF output for the Raspberry Pi. It uses the I2S sound port that connects directly to the CPU without the need for an additional USB conversion.
The HiFiBerry DAC+ Light is a high-resolution digital-to-analog converter for the Raspberry Pi. This is a special sound card for the Raspberry Pi, that is optimized for one specific use case: the best audio playback quality.