I found the big bass shacker's didn't work well with X plane, unlike the racing simulators I had been playing they gave the feel of the rumble strips on each side of the chair and made hitting the apexes very realistic. In Solange the constant rumble actually made you feel a bit sick after a while. So I put a sound bar speaker under the seat and another one behind the headrest.
They have a separate feed through a 100-watt amplifier on the back of the collective unit and can be filtered through different filters to give a very heavy base sound or to match the sound from the front speaker system. when flying the Heli in VR mode having the sound of the rotors behind you works really well.