Can't adjust BUFFER SIZE on the DDJ-RB

Dear Pioneer users/staff!

I wanted to use the PC MASTER Feature on the RB, but when I started it, there was too much latency. I tried to adjust (lower) the buffer size, but rekordbox said, that "to use the PC MASTER OUT function, change the buffer size settings". It occoured below circa 700 samples. How can I fix it?

NOTE: I updated the firmware, still no clue, what's the problem