Canton Ergo RC-L dual 9" floorstanders as subwoofer?


There's a pair of Canton Ergo RC-L for sale locally for about $600 (3900SEK).
A friend of mine said it was a good idea to run them as subwoofer only, not using the mid-range or tweeter, just the woofers, and have an active XO like the MiniDSP.

The woofers in the Ergo RC-L is 9" big and there's two of them. So there's totally four which would be equal to almost an 18" woofer.
I have not heard the RC-L myself but without the EQ box that comes with it (it has a HP subsonic filter) it's possible to get -3dB at ~18-20Hz which seems cool.

In that case I was thinking of powering them with maybe a Behringer iNuke1000 and have a MiniDSP for XO and some EQ (nasty room action at 50-55Hz).

Is this a good idea or total crap? Since they are only 260mm wide I could fit one under my bed and one either between my main speakers or along the right wall (my bed is to the left of listening position). XO at 60-70Hz and they should disappear nicely.