I've attached the M5HPOW specs below. One thing I find strange is they're spec'd to be 8 Ohms. I don't know how that's possible given the use of the HP driver.

Note they are spec'd to 55Hz and below. I suppose though that's with some chunk of wall behind them.

It may be good to but them up against a wall and see how they play. If you can't get bass out of them in that configuration, then we know something else is wrong. Maybe not enough current from your amp. After all, 94% of musical power content is bass.

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House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated