When you select "Line ( PIONEER DJ DDJ-RR) ", you can use only 0input/1output.
Now ( Ver4.2.0 ), you can select 3 outputs, but this is a software bug...
Output ② and Output ③ don't work....
①"LINE(PIONEER DJ DDJ-RR) : MASTER"
②"LINE(PIONEER DJ DDJ-RR) : PHONES" (don't work)
③"LINE(PIONEER DJ DDJ-RR) : BOOTH" (don't work)
If you want to use "MASTER OUT" and "PHONES OUT" together, you need to select "DDJ-RR ASIO".
>>whenever I use the ASIO output option, all of the audio is very crackly and not pleasant to listen to.
・Can you check the audio buffersize setting and try to adjust it larger?
・Please try to turn off "PC MASTER OUT" Button on the top of rekordbox GUI near the master volume.