Can I put the DDJ-SX or the DDJ-S1 in the DJC-SC3？

No, DJC-SC3 Soft bag provides protection for the XDJ-R1.

The DJC-SC5 bag is compatible with the DDJ-SX or the DDJ-S1.

For details about the DJC-SC5, visit the web page.

http://www.pioneerdj.com/en/product/accessories/djc-sc5/bag/overview/