When I use NI USB-8451 to communicate with STM32 as SPI, 8451 is the Master. I need the clock frequency of 8451 to be 2KHz, but when the setting is less than 48KHz, there is no clock signal of 8451. The frequency range of the 8451 is 48kHz to 12MHz?
According to the manual, the USB-8451 supports a SPI clock ranging from 48kHz to 12MHz. If you upgraded to the USB-8452, you still only have 25kHz to 50MHz. So those devices are not going to go slow enough for you.
Another option is to use an Arduino or RaspberryPi to act as your SPI controller and pass the data up to the PC over serial or Ethernet.