A one box solution is a great way to go, Marklings. I understand the desire for that. The NAD C388 is a good option. It should drive your Special Forty well.
Now, it’s not a one box solution but it’s close…. You might want consider the Yamaha A-S801 and combine it with a Bluesound Node. The Node could sit front and center on the Yamaha with either a short pair of interconnectes or a short digital cable. If you went with black you’d hardly notice the Node on the Yamaha.
Good luck with your search.
Cheers,
Scott