https://www.amazon.com/gp/product/B083B2CS38/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
 
Is the above sound card the correct sound card to get for my Audio Engine A2+ with the Audio Engine S8 Sub. Or do I need the 7.1 card too

TMatzelle60
https://www.amazon.com/gp/product/B083B2CS38/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
 
Is the above sound card the correct sound card to get for my Audio Engine A2+ with the Audio Engine S8 Sub. Or do I need the 7.1 card too

Yes.  I would recommend running the RCA output on the NU Audio Pro into the A2+ Speaker RCA inputs, then using the RCA output on the speaker to run the connectors down to the RCA input on the sub.

Yes.  That's roughly how Audio Engine describes how to connect the Sub.  You could also go from the NU Audio Pro to the Sub via the RCA and out to the speakers.  You have options. 
 
I would suggest checking with Audio Engine to see if they have a recommended setup via the RCA outputs on the card for best quality.  I would be interested in their response.

Hello,
 
I have some related questions on this topic and hope to get some advices and recommendation. I will be getting a NU Audio from Amazon very soon and want to upgrade my existing Xonar AE 7.1 to it. I am currently connecting the sound card to Audio Pro T14 via Optical out. The T14 is connected with Audio Pro Addon Sub via T14's Sub-out. Questions:
 
1) I understand that NU Audio requires SATA connection. Does it need to be a dedicated / separate connection?
2) Should I connect T14 to NU Audio via Aux out or Optical? Which will give me better sound, for both gaming and music?
3) If I am using the same 2.1 configuration, how can I adjust the subwoofer? I know Windows 10 just treat them as 2.0.
 
Thanks for your attention!