Hi, I'm trying to use R-Mix in Sonar Platinum and when launching this plug-in I see the message "This Plugin is only licenses to be used in Cakewalk SONAR X2 and above." Is the R-Mix license no longer valid for Sonar Platinum? If so, can you suggest an alternative VST plug-in with similar features?  Thank You.

What are you trying to do to your audio specifically? (btw I'm suprised you got that notice, I haven't used R-Mix in a good while but I'd be bummed if it doesn't work at all anymore)

Starting up OK here in the Feb. 2017 build .45 release

Just loaded in new project. Also added to an existing project and messed with it for a while in 2017.02. Worked OK.
 
May want to reinstall the plug-in.

Hmm. I hadn't used this for years, but I did just last week in Platinum and it worked fine.

R-mix - My one regret in not buying X2 . Anyone know if there is any way of to get hold of it now?

No, R-Mix SONAR was only available in X2 Producer. It is based on R-Mix, free standing audio editing program (not a plug-in) sold by Roland https://www.roland.com/us/products/r-mix/.
 
MashTactic looks similar to R-Mix SONAR. I have no experience with MashTactic.

I have some '80s rock stereo mixes from cassette tape and I'd like to experiment with R-Mix to extract the vocals as much as possible and enhance them separately in a separate track. I can probably do this with filters but I've used R-Mix before and it seemed really easy to use.

Usually it seems that discontinued plug-ins carry forward to new versions of Sonar but obviously not R-Mix.  Thank you including for the tip about MashTactic.
 

Thank you, I'll try reinstalling it.