There's a way to do 3rd-party-oriented sidechaining in some DAWs, without VST3, using the little-known "quad" or multi-channel features in VST2.x, if the host (and plugin) supports it. I know Reaper supports this (not sure if Waves does or Sonar does). The sidechaining I've done with C6 has been in Cubase (via VST3). 

This is the one thing that still has me clinging by a thread to Cubase and looking strongly at Studio One with its VST3 support. I'm having a serious DAW identity crisis right now. I wish I could merge the best of them all together. 

It's incredible how they all seem to be missing critical features that each other has. 

I mean, I want Cubase with Reapers audio engine, Studio One's simplicity, Logic's MIDI, unlimited inserts and sends, Sonar's smart tool, Grid and dockable UI, and MOTU's dark theme/skin. *sigh* 

We're getting close. One of these will have it all in a couple more years. It's not an endless goal. It's actually a very specific, complete, definable and doable set of fixed requirements (that each, individually, and currently, possesses) -- it's just who gets there first. And, a bunch of unforeseen cool bells-and-whistles to come, I really could not care less about. :-)  

(Or, maybe Bitwig Studio will get there first, haha.)      

I'll try looking at that. I know what you mean Jalcide - This "in between" phase is really not very productive, at least for me. I have to keep bouncing around platforms for the silliest of things. One of these days I'm going to bite the bullet and give Logic a try. I have PT but I hate it. I find Sonar much more flexible and therefore more useful when inspiration hits. Then again, it's things like these that make me think twice about it.

Reminds me of the DXi debacle. I should not have to do workarounds for things that should be the norm by now.

Noel, would you like to chime in please and tell me how I can work this out? I don't like installing and uninstalling all kinds of crap as I always get the feeling all these little workaround programs leave some sort of 'tails' in the system...

Using Reaper's multi-vst-channel per track support (not sure if Sonar also has this VST feature), I was able to get a kick sent to a bass track and was able to use Reaper's VST container to route the kick to 3/4 on the bass track -- it's pretty cool, you actually see all 4 channels pumping on that channel's meters (1/2 being the bass, 3/4 being the kick that was send to it). But, Waves C6 Sidechain VST did not seem to see the VST2.x multichannel data being thrown at it. So, perhaps Waves only implements sidechain via VST3. I'll try the test again when I have more time. If I get it working I'll try it in Sonar to see if Sonar even has a multichannel per track implementation (unless someone wants to confirm this for us). 

will x2 sidechain with any plugs other than those uncluded?

Studio One has full VST3 support and works great for sidechaining Waves plugins (Vocal Rider, Morphoder, Waves surround plugins) Also the Quantizing of audio works really great over there too. Cubase as well does VST3. (Great staff view and scoring tool there as well). I was hoping the new DP8 for windows would have VST3 but from what I've read it won't. (although DP8 for mac is currently out, the pc version is still being tested for final release)

but which 3rd party plugins are known to work with x2? (non-vst3, obv)

Pwal, I just tested a VST 2.4 compatible plugin called "The Glue" with its sidechain feature, in X2, and it worked perfectly.

I added this compressor at the end of a lead vocal bus and enabled its sidechain feature. I then added a send on a kick drum track and indeed the sidechain input of The Glue (on the vocal bus) showed up in the list to choose from/send to. Worked great.
 
The Glue is one of the best bus compressors (SSL circuit modeled) around, too. Its sidechain also has a nice HP filter that you can use to control its detector. It can also be used for general purpose compression duties, of course. But, it's also a mastering-grade tool suitable for the 2bus.

Morgan Page (a chart-topping EDM producer) uses The Glue for just this application (in Protools, which also does not have VST3). He shows it in action and speaks highly of it in this video (about 2:15 minutes in): http://www.youtube.com/watch?v=_gzKWRzCM4k

Here's The Glue by Cytomic: http://cytomic.com/glue

I'm sure other VST2.x compressors with sidechain abilities would also work.

Update/edit: Waves C6 Sidechain, sadly, does not work in non-VST3 hosts (the sidechain feature, that is). It could, but doesn't. Waves has chosen to abandon VST2.x for all its sidechain features. I also confirmed this with the Waves API2500. Its sidechain does not work in non-VST3 hosts (like X2). I then tried the API2500 in Studio One v2 and it works as expected. It shows up neatly in a section called "sidechains" at the end of the bus drop-down (nice!). I also tested the VST2.x The Glue in Studio One and it also works, and also shows up in this "sidechains" section. Man, Studio One v2 is looking NICE, I gotta say.

Back to X2. I also saw the sidechain inputs of all Softube compressor-based products show up in X2 (FET, Summit Audio, Tube-Tech, etc.). So, there are plenty of good 3rd-party sidechain options compatible with X2 (just not Waves products, which sucks). 

Just confirmed iZotope Alloy 2 sidechaining works in X2, as well.

Alloy 2 has a multi-band compressor (somewhat similar to Waves C6 but only 3 bands max) that supports per-band sidechain selection. There are two multi-band compressors in it, with 3 bands each. So, you might be able to get a full 6 bands by creative use of it.

Alloy 2 is another plugin I highly recommend. It's basically a zero-latency, low-cpu version of Ozone in a channel strip form. So, plenty of sidechaining, X2 options to be had.

firefly9000


 How nearsighted and disappointing.

a fine example of the tail wagging the dog... Sonar should be here to help us use the synths, VSTi's and plug-ins that we purchase, not dictate to us which ones we may use....

One of these days I'm going to bite the bullet and give Logic a try

yes, a DAW that's MAC only and also does not support VST3 will solve all your issues...