I have been looking at Altiverb for the past ~2yrs and was waiting for it to become available for windows.   Now it appears Ativerb 6 is available for Windows, but does anyone have it working in SONAR X3 + Windows?     

Altiverb 6 has been available for Windows for a long time. Altiverb 7 is not, even though the Mac version has been out for over two years. They keep saying they will have a Windows version at some point but I wouldn't take it too seriously. They won't even indicate a global release time, yet they keep updating the OSX version.
 
It's a shame but I think we should consider Altiverb a Mac only product. I personally use Waves IR-L, mainly because you get a nice large IR response library with it from Waves. Many people on here use a free Melda plugin, or Perfect Space/Pristine Space which was at one point included with Sonar. I guess with third party IRs, which I don't know much about. Waves IR-L is in many of their bundles by the way, and they're always having sales. I'm on a larger bundle now but I originally got it with Renaissance Maxx, a popular and not very expensive bundle (when it's on sale). Go through a site like Plugindiscounts.com for an even better price.
The IR library is a separate (voluntary) download after your purchase by the way.
 
Sorry to talk mostly about other reverbs! 

I just checked and Altiverb 7 was actually launched in January of 2010, so over FOUR YEARS ago, and while they did not specify a release date then, they said a Windows version would be forthcoming. I think that is false advertising, plain and simple. So I wouldn't bet on it ever becoming available for Windows, and if it does I'd be seriously worried about any kind of support when they move to the inevitable version 8. They plainly don't care, or they made some sort of evil deal with Apple right after they announced a Windows version.

I know I keep coming back to this but you can actually get Waves Platinum collection for like 550 now through Plugindiscounts.com (cheaper than the basic Altiverb). That includes 40 plugs, some of them dated but many still good quality and some really unique ones.

I think I had my versions mixed up.  I first looked into Altiverb when Sonar X1 was new.  I must have been looking at Altiverb 7 at that time also.  

Makes sense. I like Altiverb, but I believe the consensus is most IR based reverb plugs sound nearly identical if you use the same IRs. Altiverb does have a very high quality library. Anyway, that's why I'm happy with Waves IR-L, as it comes with a 5GB library.

Sanderxpander
Makes sense. I like Altiverb, but I believe the consensus is most IR based reverb plugs sound nearly identical if you use the same IRs. Altiverb does have a very high quality library. Anyway, that's why I'm happy with Waves IR-L, as it comes with a 5GB library.

If you purchased Alitverb and Waves, could you then import the Altiverb samples/library to Waves or is there some kind of compatibility issue?  I'm using EastWest Quantum Leap Spaces now, but it seems lacking in quantity of samples..  Can't find a small-medium drum room sound I like.

Both Altiverb and Waves use proprietary formats for their IR files so the files cannot be shared with other products.

They do both load open third party IRs though. I think their proprietary format is just copy protection, basically. I've never done much with third party IRs but supposedly there are some really good ones out there. Maybe Scook "the Answer Machine" (tm) can make a good suggestion?

Probably not. I do occasionally use MMultiBandConvolution. It comes with a very small set of IRs which I have augmented with collections from the net. Never purchased a commercial set though. Many IR download sites have come and gone. This page points to a few good free sets http://www.resoundsound.c...response-reverb-packs/