Yes, it is possible to connect instruments to the DJM-900NXS2 mixer. The DJM-900NXS2 features multiple input channels, including line inputs and phono inputs, which can accommodate various audio sources including instruments. You can connect instruments such as synthesizers, guitars, or microphones directly to the mixer using appropriate cables (such as 1/4" instrument cables or XLR cables), and then route the audio through the mixer to your desired output, such as speakers or headphones. This allows for flexibility in incorporating live instruments into your DJ setup or mixing environment.