I used a black horizontal KALLAX shelving unit for hifi set-up with a subwoofer cabinet. I had to remove an interior floor to place the subwoofer while retaining the original KALLAX design. With the small tweak, it perfectly integrates into the KALLAX compartments.
To give character … I used wood imitation tiles, glued onto the KALLAX. I added aluminum rods to strengthen the furniture design. The result is a discreet hi-fi set-up, refined and perfectly integrated.