sub recommendations for NHT Super Ones for music

I was thinking of a subwoofer for my office system which has Super Ones. Size 14 X 18. Vintage Marantz 3200 pre and Marantz 140 amp.
I have a NHT sub two in my office, not one person has ever noticed it , they think its a filing cabinet.
I'd go with a Sony WM40 (12" sub), you can pick em up new for around 130$ and used for under 100$

stuff it with some polyfill and you'll get better sound...if you want to upgrade just swap the sub out with either a HSU sub

(they go for around 50-70$ or an Adire Shiva that goes for around 60-80$)