Subwoofer Suggestion

On the cheap, you may get away with extending linearly your bass registers such as the AudioKinesis Swarm (which I believe is an great price/performance product) while maintaining cohesion and detail, but if you want both excellent performance on par with your Focals AND increased bass power, you’re going to have to spend more $ to the level of Rel or JR Audio for instance for the larger units.

I don't think this is quite correct. The Swarm is a well-thought out product and Duke has always been great at getting a lot out of his designs. I've got a pair to go with my Classic Audio Loudspeakers, which have a pair of $2000 woofers in *each* cabinet. Yet the Swarm does the trick (I'm only using a pair of them as the front speakers can fend for themselves rather well; I'm using a pair of the Swarm cabinets to break up the standing wave that is present at the listening chair).  As is the case with many things in this world, its not the cost of the thing so much as what you do with it :)

I hate to throw water on the party but if all you have to spend is $1,500 you are better of not doing a subwoofer. For that money you will never do your Focals justice. The overall effect will be worse than no subwoofer at all. A subwoofer system to match those speakers would be at least $4000.00. I would hold off till you have more to spend.

Nonsense. By what metric does $ = ♥?

A decent sub, properly implemented, increases realism beyond all proportion to the frequency response. 

ieales,

" A decent sub, properly implemented, increases realism beyond all proportion to the frequency response." I couldn't agree more. So many conversations regarding subwoofers seem to focus on bass. My experience is that properly implemented subwoofers improve everything across the audio spectrum and when done correctly you can't tell the subwoofer is on. Well, you can't tell it's doing anything, until you turn it off.

it would be a great mistake to not check out the SVS Sb 3000 sub it has the most latest technologies
it is the little brother of the great ultra 16
at $1000 beats anything at $2K 
great app for adjusting your room 18 hz
and a dual voice coil ,meaning nice tunefull bass even at lower volumes 
and a 45 day audition, and they pay shipping very compact  and a 5 yr warranty won sub of the year in 2019

@audioman58 

Yeah I'm thinking of the Sb3000 the only problem I see there is that it wont have enough output for the room. Also there's no 45 day audition here in Philippines. If ever I'm gonna go the single sub though it would be either that or the PSA V1500.