Adding Sub to current system

I currently have a pair of Sonus Faber Electa speakers. These speakers have 6" and 1" drivers respectively and have a 1st order crossover. The popular magazine test disk demonstrate the speakers go down to about 40HZ. I'm interested in what I'm missing below 40HZ besides just a non-musical "BOOM". I know for a price musical Sub's are available, but would it be an exercise in futility trying to integrate a Sub into my system? The spot I would choose for it would be to the left of my speakers in a corner - your thoughts please!
The Rel subs are musical and integrate well with most speaker systems.Even their affordable T series are terrific and designed for corner placement.
My amplification is by Krell and I found a spot next to a chair where the Sub would be open in front and back, and yes, I have heard good things about Rel - thanks!

I agree that REL subs may be on the cutting edge for this issue of corner placement, but as a general rule, many will "BOOM". I helped a friend with his ML sub, retail at well over $3000, owners manual said corner. Tried everything with adjustments, sub and pre-pro, and could not get a flat response. I was using a sound level meter and test disc with bass tracks only. We moved the sub down the side wall 1/5 of the total wall length, and was able to achieve a much better response.
Just happen to think of a trick for placement. Place the sub where you sit, and play the system. Walk around the perimeter of the room and listen. When you find a spot that has the best sound, that's where the sub goes.
To touch on the question of what your missing is questionable.
I can live with a well imaging speaker that rolls off at 40hz.
But you're missing about 10% of the music. If that much.
Good 40hz bass is MUCH better that bloated anything lower.
Sub's are very hard to blend perfectly with satalite speakers.
Once you've had full range speakers and then go the Satalite + sub, there's definatly a differance.
Just my two cents worth. John