[dsr_]

Take a look at the back of your LSR305. There's a switch marked LF Trim. (There's also a HF Trim.) It has three positions: cut, normal, and boost. It's a built in EQ designed for handling room boundaries.

You'll need to set it on both speakers.

[52-6F-62]

This, plus you could place isolation pads underneath the speakers to prevent the low frequencies from causing resonance in the desk or other platform they're on if they aren't already. You can find some pretty cheap options these days that should do the trick.