How are you powering the BM5s? They are passive, right?
I think the Headrush is closer to a PA then it is to a guitar cab, and may be why it doesn't sound the way you want. You just have to EQ it to taste. If you bought two different types of studio monitors they would sound different too. You can't really compare FRFR speakers as being equal across manufactures. All have different tone.
they are powered.
as for EQ’ing, this is going to sound stupid but is there a “universal” eq vs having to eq every single rig?