When I brought the kanta 3 home I loved the mids and highs but the bass was a mess, +10db at 100hz and -20 at 80 hz with a little recovery around 60 hz b4 falling off the chart. My room. Moving them to the long wall and playing with boundary placement did smooth them out a lot, but they never did offer much below 70 hz in my room. I would try a single sub between the speakers first and if that don't work then buy the second. A flat measuring speaker isn't necessarily desirable and the Kanta only needs help with the bottom 2 octaves.
Subwoofer Suggestion
Hi guys I need your suggestion regarding subwoofers. My system is composed of Focal Kanta 3, Kanta center, 706BK it would be used 50/50 for music and HT. My room size would be 13m by 4m by 3(Length,width,height). Would it be better to go for dual pb1000/sb1000 or single sb3000 or single pb2000 or single PSA S1500?