Hi, i'm having a problem with the volume level of garritan cfx. I use the following setup: 

Yamaha Avantgrand N1 connected via midi to a steinberg ur22 mkii and then via usb to a macbook pro 2017. I then use either the heaphone output on the mac or that on the steinberg to listen back while playing. The problem being, that even with master level at maximum, the sound is way too low than the internal one of the piano, to the extent it is barely playble.

However, I tried playing some midi files through garritan player and they sound quite fine, as far as volume level is concerned, so it seems like it's a problem of my midi input. The cable used is a cordal. I use sennheiser hd599 as heaphones, which have not a high impedence. Moreover, the same happens with the internal mac speaker which usually have high volum output. 

What might be the problem?

Thank you for your help