Complete newbie (as will be obvious by my question): I have Sonar 6 which I'm having trouble getting to work with Windows 10 (on a new computer). It doesn't seem to recognize my sound card... (software works, unit turns on, but no sound to headphones). If I upgrade to Sonar Artist, will it still work with my Cakewalk UA-25 EX unit?

Yes as long as there are drivers for it for Windows 10. I found this https://www.roland.com/us...cts/ua-25ex/downloads/

The absolute best way to find out is to download and try the Demo. 

http://www.cakewalk.com/Products/SONAR/Try-SONAR#start

You need to get your audio interface/sondcard working in Windows first before Sonar can access it. Otherwise upgrading Sonar won't make any difference.