SPA stands for Stereo Power Amplifier. This module is a modified Power amplifier DA input module where the amplifier always selects the analogue input (balanced or unbalanced) by means of a modified firmware version and the volume is at its maximum. This makes the module usable as a power amplifier. On request, it is also possible to select one of the two digital inputs instead of the analogue input, so that the power amplifier can be used as a power amplifier in a full digital setup. Think of a system with an external DSP board.