I need help with an amp decision

What kind of sound characteristics are you looking for?

soix’s question is a key one, as is the budget for the amp

afaik, nelson's first watts don’t run balanced ins in standard stereo configuration -- (e.g. the f4 has a balanced in, but it is used only if run as a monoblock)

Consider monoblocs and getting a second sub.

Consider an NAD C298.  It is $2K new.  I just took one of these in on trade and am NAD dealer so I have spent some time with it.   It is stupidly good for the money.  IMO...maybe the best amp you will find under $3k.  It is Class D but you won't know.  It needs a little time to burn in but this amp is far better than you would think.  Not a hint of brightness and will deliver wonderful, controlled bass with lots of detail.  

You may struggle to find this used not because they don't come up.  Mine sold in 5 minutes.  This is the same amp in the M33 which one product of the year and sounds incredible.

Another option would be the Rogue Hydra.  Lists for $3K and can be had in the $1500 to $1800 range used.  You will want to swap in NOS tubes if it still has the stock JJs.  A pair of NOS Cifte/Mazdas or Mullards will make the amp shine like the sun.  And, since it is class D, it behaves like SS and the tubes need to be replaced every few years at most.  

As I mentioned above, I am an NAD dealer.  I have no affiliation with Rogue.  I just personally have owned a Hydra for several years.  

Thank you for the feedback so far. Sound characteristics for the amp would be a good sound stage along with a neutral presentation. My room cannot be sound treated to my liking and I'm a little sensitive to treble so the amp cannot be harsh to the ear. Monoblocs and another sub is the goal but is a future goal. For right now my budget is about 2k in the used market. Thank you for the suggestion on the NAD and Rogue, I will look them up.