I'm working on some block diagrams for this, but they are not ready yet. However, in more simplistic form, here are the audio paths for receive.
This is the path when you use the audio connections on the radio:
Antenna --> RF ADC --> FPGA --> Ethernet --> PowerSDR on your PC --> Ethernet --> FPGA --> Audio DAC --> Speaker/Headphones/Line Out
This is the path when you use VAC and an audio interface on the PC:
Antenna --> RF ADC --> FPGA --> Ethernet --> PowerSDR on your PC --> PC Sound Card DAC --> Speaker/Headphones/Etc.
However, again, remember that the VAC interface is a bit funny as it was originally designed primarily for digital mode operations, which is why VAC1 carries RX1 ONLY and VAC2 carries RX2 ONLY. It's only been relatively recently that people have started to use VAC and the PC for "normal" op's. What we really need is a "VAC0" that duplicates the audio stream sent to the radio (keeping VAC1 and VAC2 for digi op's).
Read my
tutorial for more detail on how to use the VAC interface.
73,
Scott