Hi @Anonymous User
Yes you can use any supported device when you sign up to NowTV.
List here
https://help.nowtv.com/article/what-devices-can-i-use-to-watch-now-tv
However the white nowtv box is getting a bit long in the tooth now and you may need to look at a replacement update in the near future (maybe a smart stick when they become available sometime in Feb) ?
Edit ~ When you say an old set top box i am assuming a white nowtv box ?
