Are we looking at the same graphs? Your -6dB point is 8Hz, but at 5Hz you're -18dB from the peak of your response @ 25Hz. It's the slope that I'm most concerned with, as that's the indicator that below 10Hz, your output is dropping quickly. That's what my previous comment was referring to, since in the past you've been all about that super deep stuff. This response shows you're not getting the super deep stuff.
Since you just got new calibrated testing equipment, and you're outputting tones via HDMI, I doubt anything is off. It just is what it is, and it's not magic.