Subwoofer design has never been a strength in Meridian's product portfolio. Over the years the subwoofer designs Meridian have offered would all be better described as add-on woofer systems than true subwoofers. They simply don't reach down low enough or offer sufficient output at the bottom of their passband. As Caldham implied their best to date, the D2500 and D5500, have not outperformed the low-end capabilities of the larger DSP loudspeakers in the line.

So all of us keen to own subwoofers that truly live up the standard of the larger Meridian DSP loudspeakers have had to purchase subs from companies like those you mention (and others- see my signature) and then ensure our pre-processors have the necessary compliment of both digital and analog outputs to support this configuration.

Happy Trails!
MTB Vince

2ch: Jay's Audio CDT2 Mk3, PS DirectStream Dac, Oracle Delphi VI/SME V/Benz LP-S, Coincident Statement Linestage, Foundation Research V5 Phono, JL Audio CR-1 xover
M-ch: OppoMod 203, Anthem AVM60, 2x 557
2x or 5x ATC SCM20ASL mk2, 4x SCM12i, 4x Seaton Submersive HP, AM2.0 sub EQ
Video: JVC X990, Isco 3L A-lens/sled, 105" motorized 2.37:1 AT screen