Subwoofer with Floorstanding Speakers?

I suggest you first consider a single SF Gravis V not because its an SF product rather for the flexibility its accompanying application can provide regardless of speakers its paired with. 

Without any personal experience with the Gravis I question it's -6dB frequency response rating. Without having read its application instructions if it has auto calibration it makes for far less manual adjustments. It appears to include four customizable presets and assuming the application offers remote control of adjustments and volume. I've found this combination allows a subwoofer interactive flexibility that I can't live without and worth most any increase in expense.  

With the subwoofer placed at the listening position playing a low frequency cadence you should be able to identify your rooms bass modes by simply strolling around. The loudest mode becoming the subs location should provide a single sub adequate performance at the listening position. Later the Gravis V can serve as the master for most any more economical non processing sub. They need not match.

Have fun with it.   

It appears that your Olympica Nova V's can be bi-amped. You might want to start by trying that to see if that adds enough low end to your rock recordings. Integration would be far simpler. Separate gain control with each amp would be required for best results. Without it there might not be a noticeable difference.

Your Nova Vs go to 32Hz, but that is already down a few db. So yes, there is information below that point, lots of information on some records. Although 32 Hz is pretty good, lower than that is better. 

Bass is the backbone upon which the rest of the music rides on. Up until the mid 80’s subs weren’t needed. Then the Mfgs etc started pushing midrange because it has the majority of the music.R&Rollers weren’t considered in this because classical and jazz were the accepted genres. In doing so, they robbed the bass from the speakers so that now, even a supposed full range speaker needs a sub for life of the music. It took me a while to accept that but i have run subs for 20 yrs and choose Rel as THE sub IMO. As has been said, pairs are better and the Rels add so much more to the music, IE sound stage and make the speakers sound bigger.And they are very easy to integrate. Depending on your room size, there as a Sumiko S10 for sale which is the Rel S5 clone. It operates in the same way as Rel and Suniko was the distributor here in the US for many years.and somehow pretty much copied the Rel ,,, at least for a year. .

BTW no affiliation with the seller. Just familiar with them and have them myself

I use a pair of Martin Logan Depth i, in my small room. It’s vibration cancelling design is why I chose them. Using Stillpoints SS underneath them. Good tt decoupling is a big help