X99 Killer MB Sensor 1 Very Hot

Given what I have read about the Corsair Link software, I would not trust it. It is known to be full of bugs, at least in the past.

That said, most of the readings shown seem reasonable. That does not mean I trust it yet. But the main problem is, what is "Temp #1", etc, actually reading? Also, what is Temp #2 and Temp #3?

Without knowing what it is reading, it is impossible to make a judgement about something being too hot or not.

For example, that might be the X99 chipset temperature. 57C is somewhat high for the chipset temperature (the maximum is at least 100C), but that could just be caused by poor ventilation in the area of the chipset.

That might be the CPU VRM temperature, which tend to run warmer when using AIO liquid coolers, since they don't provide any air circulation in that area of a mother board. Of course that depends upon where the radiator is mounted, whether you are running its fans as push or pull, what PC case you are using and the location of case fans, etc. You did not provide any details about your system that would help with that.

Does the Temp #1 reading change at all? It is possible that reading is an unused sensor on the sensor chip in your board.

Try running another hardware monitoring program, like HWiNFO64. It is much better at identifying what sensor output it is reading. Try to match the Temp #1 reading with a reading in its Sensor display.