Low volumen leves on DDJ-SZ

Hello guys, I own a Pioneer DDJ-SX & Pioneer DDJ-SZ. I been having volume issues with the SZ. when I use the SX, I don't have any issues. but when I use the SZ, it seems to me like I have to push it in order for it to sound loud. for example. when I record a mix on SX, everything is fine. I have my channel 1 &2 at about 12 o'clock and the record volume on Serato dj at about 1/2 way. when I record on SZ, I have to turn down the channel 1 & 2 to about 11 o'clock and I have to turn up the record volume on serato dj at about 75% in order for the yellow lights in the meter to turn on. for some weird reason it feel like the SZ doesn't have any power. can you help? I love the SZ very much but I feel disappointed and I'm in the verge of selling it.

I have a MacBook Pro

OS X El Capitan 10.11.6

8 gb ram

Searto Dj 1.9.3