This has been said, but it probably needs to be said more often – Roon is not JRiver. Many people come to Roon from JRiver and hold various assumptions on the basis of JRiver. Just because JRiver does something a certain way does not make it correct, nor that Roon should do likewise.
Take surround processing or upmixing, for example. You assumed that Roon does surround processing similar to that of JRiver. Yes, JRiver does it, but that does not mean Roon or even JRiver should do it. Roon and JRiver are not recognized experts in surround processing. And I, for one, am dubious about time and effort spent on any homespun solution. If Roon wants to add surround processing, license a known surround processing routine from Dolby, DTS, Meridian, Lexicon, et al.
That polemic aside, we want to help you get to the bottom of your issue. Others have experienced like issues with multichannel mapping. Try reading this thread and following its troubleshooting advice. Roon developers chimed in and confirmed that Roon is observing what is closest to the de facto standard for 7.1 channel mapping.
AJ