I guess my main confusion is, in what capacity is the standard SPI protocol supposed to work if it doesn't work with any devices that require more than messages longer than 8-bit? I would imagine that the amount of devices that need messages longer than 8-bit far surpass the amount that need exactly 8 bits, unless i'm misunderstanding something.
For clarity, this is exactly what the documentation of the slave i'm using says:
"On this device, an SPI bus is used to set device configurations, operating parameters, and read out
diagnostic information. The SPI operates in slave mode and connects to a master controller. The SPI input data
(SDI) word consists of a 16-bit word, with a 5-bit command and 11 bits of data. The SPI output data (SDO) word
consists of 11-bit register data. The first 5 bits are don’t care bits."
Is there a reason a standard SPI setup wouldn't be capable of meeting these requirements?