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!