Subwoofer for Kef LS50 Wireless II?

OK, missioncoonery. You must be an expert. Just gave my opinion from MY experience.

How are you going about it?

I have Ls50 metas and a Klipsch sw308 sub in a smaller 12x12 room. Larger rooms are likely more of a challenge in that the sub will have to do more. Listening to my ls50/sub combo as I type. To get the sub set up right I used a sound meter app (decibel) on my iPhone to fill in the lowest octave that was missing in my case mostly below 40hz or so. You need to measure to get it right. I had crossover set way too high by ear. Using a white noise streamed internet channel as the source I Turned up sub level then adjusted crossover point and tweaked those two until low end was leveled with the rest. Then tweaked phase with some good percussion recordings for best dynamics. Could not have done it right by ear alone. Sounds awesome. Sub needs to be able to go down to 20hz or so in your room to fill in the bass completely. Check the specs. The new KEF sub is designed to go with the ls50s. I’d look at that first.

@midareff1 recently tested a couple of Martin Logan Dynamo 800x subs with his very nice music only system. Long story short, he absolutely loved them.

I have 4 REL S510 subs in our large room. Using the high level connection. Sounds fantastic. 

I spent a good amount of time trying to integrate my two SVS subs into my system.  My main speakers are a brand of towers not sold in the U.S., but are 2 1/2 way with all scanspeak classic drivers; a 1" soft dome tweeter and two 7" midwoofers.  So they put out some bass on their own.

I was following the time honored wisdom that the bass should not stand out if the subwoofer is properly integrated, you only notice it when the subwoofers are turned off.  After more time than I care to mention trying to implement this "integration" advice, I just cranked up the subs gain (volume) to a non time honored advice level.  That was what was needed.  This is not akin to the type of bass you hear from the inside of a teenager's car. 

My listening pleasure is mostly rock, and I now clearly hear the bass guitar and bass drum setting the beat down low when they do their thing.  Just as I would at a live concert.  JMHO, YMMV