Subwoofer Level Control

I have my ICBM connected between a SACD player and Denon 3300 receiver. I have L/R recombine switch set to off. All connected channels have crossovers set (no bypasses).Sub is connected to ICBM. As I increase the level of the Sub level control the bass in my "normal" speakers increase significantly. I thought that this control was only for the sub function. How is this control supposed to function and is what I'm experiencing normal?? Thanx

I'm a dummie .... I was hearing sub level go up. I turned off sub and turned up sub level and heard no bass boost in main speakers like I thought I was. It's amazing how you can be fooled by the non-directional sub output.