Take a look at Rythmik’s F15HP, a lot of bang for the buck. If you want to keep things closer to $1K, the F12SE. While I use 4 subs in my main system, unless you’re planning to really rock out while you’re working or have a huge office, I don’t think you need 2 or 4 subs in an office. If you just want to add in some low level information that your main speakers can’t provide, a single sub can work fine in a smaller room. I have 3 smaller systems, each with a single sub (all are sealed subs) and they all sound great for their purpose.