In both 32 and 64 bit Splat, RX4 shows up under "Utilities", bit in 64 it says "Cannot perform function" when I try to use it.
Anyone know why?
P.S. I already forget how I got Sonar how to recognize RX4 as editor to begin with!

I used daily RX4 (and now I use RX5) in Sonnar 64 Bit.
Always with RX 4/5 Connect.

For me it never worked with the utilities menu.

Mark a part of a clip  -->  RX4/5 Connect (OK) --> Working in RX4/5
After Editing --> Send Back  --> RX4/5 Connect (OK) --> Done
 

I forgot all about RX connect!
It wouldn't work for me back when  i got it- now I need to revisit it.
 
thanks!

RX Connect never worked well for me within Sonar but RX5 has worked ok added to the utilities menu. iZotope has some info on how to use RX5 within various hosts. It refers to RX4 but I believe it is still relevant to RX5. One of the Sonar hosts has created a small utility to make the process easier if you decide to go that route.
 
https://www.izotope.com/en/support/knowledge-base/rx-connect-faq.html
 
 

RX 4 Advanced has always worked flawlessly as the editor under utilities- but I've been using 32bit Splat.
It replaces the audio exactly where it was after editing- very quick and easy.  
 
As I write, I'm trying to use RX Connect.....
NO DICE.
 
I tried it with VST2 and VST3 versions in my menu.
THambrecht, perhaps you could elaborate a little on how you are using RX5?
for example, what do you mean by, "mark part of a clip"?

Go to the Software forum ad check out the first stickie thread. You'll find a link to scook's rogram that will add any program (audio editor) to Sonars Utlity menu.

Follow the link to Scook's Tools and look for
http://forum.cakewalk.com...tilities-m3392713.aspx

Scook's Tools:

SONARToolsEditor by scook
Use the Download link on that page.