Aurender Model Choices

I own an Aurrender N100 and W20SE and have had significant exposure to the N10 and N20 as well as a number competing streamers. Aurrender would always be my choice. In general, each level represents a substantial improvement in sound quality, in all respects. More detailed, natural, lower noice floor, dynamics, and imaging. My digital end and my excellent analog end provide equal sound quality (see my virtual systems).

You will get better sound quality from an N20 than from a N200. In your set up the N20 will sound better, but it is likely to sound significantly better if your preamp and amp were higher quality. So, I think the question to ask is if you are on the path to a better system and will be upgrading your preamp and amp at some point, then N20 is the way to go. If you will stay with the benchmark stuff, then N200.

I’ve had Harbeth speakers with Benchmark electronics and think it is an awesome combination.  Very synergistic.  That said, Harbeth loudspeakers are not the most revealing speakers (the monitor series are a little more so).  I think you would not hear a lot of difference between any of these streamers.  At the level of your system, while very good but one I would describe as more musical than analytical, when choosing a streamer I would consider which features you want in the streamer more than sound differences (and therefore recommend you look at others in addition to Aurender).
   WRT Aurender, they are excellent for sure.  I’ve owned both the N200 and N20.  The biggest difference between the two is that the N20 has a superior OCXO clock in it (which is only used if you use the SPDIF or AES output) and also does upsampling on the fly.  Otherwise if you are going to use USB output I would not personally splurge for the N20.  Even then, the N150 might suit just fine.  If your dealer is willing try to borrow them and see (hear) for yourself.  
    I mentioned features being what I would recommend looking at at this level above potential sound quality.  These include desired interface (Roon vs Aurender Conductor vs Innuous sense, etc.), upsampling/downsampling capablity (very robust in Lumin products for example), outputs available (USB, SPDIF or AES/EBU) compared to what may be the best input on your DAC, streamers having inboard storage (aurender) vs requiring an outboard server (Lumin), and such things.  There are so many permutations that unfortunately it may take owning a few of these different manufacturers’ models before really understanding what you like best.  
    But overall I think finding a streamer that suits your needs and preferences will give you more satisfaction.  Before spending a lot of cash on a more expensive streamer I would try to hear in your own system if the differences in sound between streamers are that obvious.  Dealers will tell you the N20 is leaps and bounds above the 200, and it is great - IF your system and room allows you to use it to its potential and you can hear a difference via your system.  

Sorry, you asked what differences between the N200 and N20.  When I used the N20 AES output upsampled, driving either a Denafrips Terminator (also using its upsampling) or Mojo audio DAC, compared to the N200 the sound is cleaner, clearer, more refined overall.  These traits I value and one reason I liked the Benchmark equipment with Harbeth.  Once I got a DAC that I would be using only USB with, I went to the N200.  USB input will use the clock in your DAC as opposed to the one in the streamer.