Do I need a sub?

Get a adapter w two male 1 female , plug adapter in back of main out of preamp, then run single shielded rca to sub?

easier this way? this will just dump everything over a certain freq to sub?

 Or use the speaker terminals which will remove the low freq going to the speakers (towers) and allow a little louder volume,by not sending lower freq to the smalldual 6” woofers???

You need a sub with a high pass filter. With that BIC V 1020 you will have to run your speakers full range!

Get one or two used RELs (or a swarm system if you have the space as they're alleged to work) and don't bother with the silliness of limiting the output to the main speakers and just 'em run within their limits. I used a single REL Q150e (10" front firing 150 watts) for a couple of years bought for 200 bucks (used of course...Ebay)...still works perfectly, and added a REL Q108MKII (100 watts down firing 8") later...also 200 bucks. You don't need to do anything but hook 'em to the amp's speaker jacks, and move them around until they sound good to you (putting one in your listening seat is unnecessary, and takes some long cables). Note that good subs add air to the proceedings by sort of "charging" the room and make even bass shy stuff simply sound like real music...it's not just about organ bass notes and EDM (although hey...).

I really kicked around the idea of a swarm set up for subwoofers.
Spent lots of time researching and reading about what it would take to do it, what parts I would need, what approach etc etc...

I decided to just go ahead and add two purportedly nice sounding subs to what I have now.

The subs I bought are HSU ULS-15mk2`s. I have the tracking numbers sitting here.
I like Rythmik and used one with some MMG`s (my daughter now has it)
but the price to performance ratio just didn`t work for me.

Anyway..I`ll have 4 subwoofers in all. A Revel Ultima15, the two 15" HSU`s and to tuck away somewhere as needed 10" 350 watt sub.
All sealed.
Should be interesting in my 3840 cu ft room

Found a great price, so I bought 4 of them.
one for my cousin.

 
 If I hook up via speaker wire, doesn’t this push the low freq from the main towers to the sub?
or still full range for towers?