Do I need a subwoofer? Which brand and model?

Quick update - subwoofer arrived along with "reference" music. Reference music was a huge disappointment. Had to go back to my Bill Evans Waltz for Debby hi-res from HDTracks. Cable not here yet so cannot set subwoofer up but just one comment - it is much bigger than I thought it would be, and I'm glad I did not order the SB12 Plus Ultra, as it would have probably resulted in divorce papers :)

The build quality is fantastic - beyond my expectations. it's heavy too. I ordered the piano black finish by the way. Will let you know how it sounds after cables arrive.

Finally set everything up today. I was confused about the cables (got a single one from Blue Jeans, then had to order a Y adapter to connect to the stereo outputs). Also, you cannot connect this to Pre 1 on the NAD as there is a hard connection (bridge?) between that and Main, and no sound comes out of your front speakers if you take it out. NAD has a handy Pre 2 with a volume control on its own :) Having figured this out, next challenge was the settings on the sub itself. Initially, the presence was not felt or very minimal. I put the frequency to LFE, the Phase to the other end of 180 degrees (0 degrees ?), and the volume on both pre and sub to max. Now it is making its presence felt :) I can distinctly hear the bass guitars on it, much more pronounced than I ever have. This is precisely the aspect my friends had complained about, Current placement is left of left front speaker, pointing towards center of room where current listening position is. SVS recommends putting it in the corner of the room, which I can also try. For the moment, I am happy, but I will need to keep tweaking and start measuring. I also changed the cables between the Oppo and the NAD amp with a Blue Jeans stereo cable, separately, and that had already improved the sound level at least. I am now a believer in subs and am already looking forward to a second! Also, I am wondering if an audiophile grade rack (not a bank breaker) would further improve anything. I need a new rack for better organization, but was wondering about an audio one. Thoughts welcome,

I am getting my turntable back and will conduct some digital vs audio tests in the near future. Also, I am thinking of adding a tube phono stage to the setup - thinking of a Bellari VP 130 which has good reviews for bang for buck. Thoughts welcome.

Wow! It makes a significant difference to the sound of the piano as well!