SPI communication between MCU and slaves
To reduce pin count, the normal way would be to use a demultiplexer that take 3 pin binary code and gives out 8 pin individual signals. Such as 74HC251. 

That is, you can't use any "automatic /SS" features of SPI but must handle /SS manually by setting 3 pins. Optionally use a 4th pin to the /CS of the demux if you want to shut off all communication with no slave selected.

MOSI, MISO and clock are all connected to all nodes with no logic in between.