Typically, they look for at least 100-dB isolation.
The converter only needs a power supply and some clocks. Feed it some audio analog and the device will do the conversion and output digital audio in the form of I2S or left justified depending on the part.
Consequently, the cost per channel can be significantly reduced by using the eight-channel device.
The CS5343 provides higher performance than the CS5330A/1A yet it is smaller and more cost effective compared to the CS5340/41.