Which subwoofer?

https://www.parts-express.com/10-Wireless-Subwoofer-Package-with-Dayton-Audio-SUB-1000-300-5792

2-4 will work just fine. You'll be good to 25 or lower and cut the ML at 40-50.

You will enjoy FAST clearer BASS. 

That Mac has tone control, use it to get things right..

Room treatment, in a small room is a must... Thick floor to ceiling curtains work VERY well and help to dampen the room by opening and closing them. NOT just the curtain,. Windows and DOOR can be opened to release pressure too. Curtains will still dampen the opening..

1-400 watt 8 ohm plate amps get LOUD..  I use to hit the bump stops with a 12", 15", and a 15" passive drivers in 6 cf boxes all the time 125/250 watt plate amps. 18hz to 250 hz clear as could be..
VMPS RE- powered subs.. great value too.

My design was and still is very close.. I like using passives to really tune the blend the subs with the BASS. I use to use Mor-tite weather seal and pinch putty to get it JUST right.. (stays soft for 20 years)

NOW with DSP "perfect" is almost doable.. if you like it PERFECT.. :-)

GRs OB servos are the cat meow. I use them about 60 hz down, and with MB columns phase plug tuned.
That is how I balance the weight of the bass. I like 80-280 or so..to be VERY fast.. I direct couple those drivers to BIG amps and use active XOs with full blown DSP multi xo points,  threshold, summation, on the fly correction and mic feed for OTF correction and testing..

Just so you know there is NO dampening when there is anything between the amp and the drivers.. That includes a passive XO.. NO DAMPENING.. No mater what you think.. ZERO.. My way it does.. just that simple. I'm not the only one either.. look around.. IF they will share..

I use to use VMPSs bass design, man were they easy for a passive design and DEEP bass. I still do when I need chest compressions..

They will do it..

GRs though.. just night and day how they work and pressure a room.
bdp24 couldn’t have said it better. When I coupled that system with MB columns.. I really got happy for the first time in a LONG time.. Man oh man does it work.. of course Planars and ribbons for the monitors sections.. again separate enclosures.. Lot of real estate though.. BUT you can actually get the sound perfect for your ears..

Where’s my transistor radio, go do a little sanding in the shop..
Clear coating plinths for the 124s.