The Flex Eight is a tiny box. We just couldn't fit everything inside it along with the toaster and coffee maker some of you expected.. ;-) 

If you need analog input for your configuration, the easiest way is to simply purchase an Analog to Digital Converter (ADC) unit. These are quite common on online shops and typically output SPDIF/TOSLINK and will therefore perfectly fit with the multiple digital inputs of your Flex Eight. Final audio chain will be: 

RCA/Balanced input - > 3rd Party ADC box - > SPDIF/TOSLINK input of the Flex Eight - > DSP - > Analog out