I haven't heard Omen bookshelf but I do have Omen DW's which I love. I would imagine the bookshelf version gives a very big sound like the full size Omens minus the bass extension that the Zu Griewe cabinet loading gives.
My Zu DefHeads are also sealed cabinets rated down to 50hz just like Omen bookshelf. They sound huge and I don't ever feel the need for a subwoofer for them.