I use an SVS SB16-Ultra subwoofer with my Klipsch RF-7II. (Left, center, and right are RF-7II, plus an RF-7 for the rear). I also have a Klipsch R-115SW subwoofer in this system. Tube amps. I use this system for hi-res surround-sound recordings of classical music.
I use my Oppo UDP-205 universal player's "bass management" - i.e., a built-in configurable crossover, and a connection for a powered subwoofer. With Oppo's bass management, the low frequencies are off-loaded from the main amp and speakers, thereby facilitating greater overall dynamics.
The plate amp in my SVS SB16-Ultra quit working. SVS provided excellent customer service. They shipped a replacement amp, which was fairly easy to install. I'm satisfied with the SVS SB16-Ultra.
With the 2 powered subs (15" and 16"), I have ample low frequency power for large scale orchestral music.