DJM 900 NXS2

only 3 words......why?

ok....Why are the highs are weak even when I have the fullest

Not exactly sure what you mean. First it depends on the Quality of your source and the subjective Feeling...

i.e. I am not thinking the highs are weak.

For better understanding it might make sense you will upload a Sound example somewhere which can demonstrate the Sound your getting.

It would help as well to know what your source is (i.e. Phone, CDJ, other) and if it is a digital file Format you are using. If yes what Format is it? Bitrates?

This will not solve your issue but we probably can understand the real issue. 

DJM 900 NXS2 + CDJ 2000 NXS2 + YAMAHA HS8..... MP3 320 bitrate.

Get better tweeters.