SOUND QUALITY CHANGES - RMX 1000 , EFX 1000

Hi everybody!

I saw this problem in past (2012) , but nobody knew the solution, so i wonder if it is solved now. 

So, i have connected rmx 1000 in the mixer through send and return option. And when i press the yellow efx button on the DJM , sound changes. It is not as clear , not as crisp, just a little bit , but it is clearly low quality. 

It happens on the efx 1000 and also on the rmx 1000.

I had rmx 1000 2 years ago and when this happend i tought that rmx 1000 is inferior to efx 1000 in sound and i sell it and bought efx 1000 , just because this issue. So it is not so little noticabe. And now when i saw the same happens to efx 1000 , i sold it too, and bought rmx 1000 again . 

And now i really expect some kind of solution. And i am sure a lot of users have the same problem. 

Thank you very much for solutions.

Marko