Combining a sub-woofer with Bookshelf Speakers

So my speakers are small Cabasse Galiote bookshelf model. Great sound, but little bass. I've been working to combine a REL (Q201E) sub-woofer with them.

The Galiotes technically reproduce 70-20KHZ, but the frequency response curves, as far as I've been able to find them ( the speakers are 30+ years old) suggest there's little below about 100HZ. So I set the roll-off at max (106HZ, I believe) and reduced the Hi-Gain to a very low level (to avoid 'boom').

I'm listening, and it sounds good to me. But does anyone else have experience trying to do this type of thing?

Let me know any thoughts.