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!
Corner placement of a sub will give you the most non-musical "BOOM". Back wall or side wall away from corner will be a better response. What amp is driving your speakers?
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.