These cabinets certainly look good! What dimensions are they? How big and how long is the port? Did I understand you correctly in that you used the Delta PRO 15 on these?

I just ran the numbers in Boxplot for the Delta Pro 15. At best they'll go down to around 40 Hz with a 8.5 cubic foot cabinet tuned to 42 Hz. I'll be able to tell you what your box and port do once you give me the numbers for your cabinet including wall thickness. I suspect that this driver isn't going to deliver the kind of bass you're used to from your Kilomax 15. Its a different animal with quite different specs.

One other thing to consider - room acoustics. Walls appear to be brick from the picture, which will likely bring out the highs allot more from all the reflections off the walls. Also, are these situated in a basement, perhaps on a concrete floor covered with thin carpeting? I'd be willing to bet that if they were parked on the floor of a different room on the main or upstairs floors, you'll notice quite a difference in the bass. Don't ask me to explain it... I'm no master of physics. But I do know the profound effect that the resonances of wood floors have on the sound of my Premium Stage Four Pis and also on the bass drum of my drumset!

Regards,
Colin