before I got done reading your whole comment my thoughts were you should probably just use the RX noise to fix the tracks then bring in them in to Sonar after. but you can also use RX as a plug in and bounce it "freeze per say".
just make a back up copy if your going to use RX destructively = "Bounce/use clip FX".
 
- set up RX like you want it, then press the freeze button in the track.
- put RX in the clip FX bin and bounce it destructively.
- fix it outside of sonar, then bring it in by way of import.
 
I always choose to fix clips outside of Sonar, then drag them in via the browser.
but its your choice. good luck.
 

Some RX functions (not all) place a very high load on your CPU. There are "preview" modes but in my studio, even with a very capable i7 machine with lots of memory, there are some RX processes that simply can't be done reliably in real time - even if the host itself has a very light "footprint" (e.g., Sound Forge). 
 
I'd be interested to hear what happens if you migrate the same project with the same plug-ins, all with the exact same settings, into Reaper. My experience is that a CPU-hungry plug-in is a CPU-hungry plug-in, regardless of the host.
 

Thanks guys for your answer. I am would also like to do what Anderton asked about migrating the same project to Reaper just for the sake of checking the cpu management. I will try to do it, but as I said I am just a hobbist and with very few time to use my homestudio, and I think all of you know how much work it is involved in migrating a project from one DAW to another, I mean you basically must do everything from scratch.
 
I will se if I can save each plugin setting in each track, then create create a project in reaper with the same 24bit/44.1KHz wavs and see it how it behave. I will share with you my results once I do that.
 
I also replied to Keith Albright and I will send the cwb to him so he could take a look if is it any improvement that could be done.
 
Thanks everyone for your attention to this issue. Also sorry for my sometimes hard to understand english... I am a spanish speaker and my english is not all that polished as I would.

To freeze only Izoptope Rx, assuming it's first in the chain, you can just do this:
 
1. Temporarily bypass the plugins you plan to keep active.
2. Freeze the track with Izotope Rx active.
3. Un-bypass the other plugins.
 
I don't see how any DAW could selectively freeze the contribution of one plugin in the middle of a chain without also freezing everything upstream of it. Freezing the processing of a single plugin is automatically going to effectively move it to the head of the chain. If it isn't already there to start with, the sound of the track is likely to change.

brundlefly
To freeze only Izoptope Rx, assuming it's first in the chain, you can just do this:
 
1. Temporarily bypass the plugins you plan to keep active.
2. Freeze the track with Izotope Rx active.
3. Un-bypass the other plugins.
 

 
Thank you very much for your reply, this is exactly what I need to do. It is a shame that I didn't figure out by myself. And about freezing only specific plugins I meant exactly what you told, being able to choose until which plugin in your chain you want to freeze. I understand that it is imposible, and also it doesn't make sense, to selectively freeze some non-contiguous plugins in the FX'x bin.

I added [Solved] because Brundlefly's answer is very helpful, and people search on [Solved] to find answers. If you don't feel this is justified, I can remove it.

Quick follow up with the OP. When you say "Izotope RX-Noise" are you referring to "iZotope RX 5 Dialogue De-noise" plugin? The reason I ask is because I got the RX Plugin Pack is part of software I am evaluating this weekend, and the "iZotope RX 5 Dialogue De-noise" is part of that.
 
If this is the plugin, it is definitely not one I would ever run end-to-end on any track. Once noise and intended audio overlap, there is no way to differentiate the two, and no way to determine the assumptions it is making internally. Removing noise as surgically as possible requires the noise alone to be analyze (captured), and then removed from the track. This is a very manual and intentional process that should be done on a raw audio track (no other FX whatsoever), and requires the audio to have an isolated "noise only" portion (either a lead, tail, or section between phrases).
 
From the perspective of noise removal, *if* noise is consistent and can be isolated, you can take a sample of that to remove it from the entire track. This plugin can come very close to how I do it, but requires use in "Manual" mode on an isolated noise portion. This is also something I would definitely do to a raw track (no other effects whatsoever), and then bake in (i.e. bounce to a new track) once done.
 
Assuming you have a lead/tail/section of "just noise," you can:

1. Insert iZotope RX 5 Dialogue De-noise on a raw track
2. Position the now time so the transport will *only* pass over the isolated noise
3. Set up the plugin to "Manual" and click "Learn"
4. Start the transport and either stop the transport or disable "Learn" before audio hits the plugin (this way only the noise is analyzed)
5. Bounce the track to a new track with the embedded FX being processed

The above process comes as close as possible to the "Capture Noise Print"/"Remove Noise Print" that I do on a regular basis, but is rather clunky, takes 5 times longer to process, and requires the transport to be running to do the capture. However, it is a good option for removing noise, but not something to insert and run end-to-end in "Auto" mode.