Hello I am awaiting my new Acoustic Energy AESprit 309 floorstanding speakers to arrive but wanted to know if anyone know's how these are mass-loaded for better bass resonance etc... I know there's a port @ the bottom of the rear of the speaker but does this already come pre-filled or do i need to buy Atabites or similar and then pour them in as i have done in the past with stands for my B&W stand-mount speakers? Thanks for advice