I've been using Sonar 7 Producer Edition and recently upgraded to Sonar 8 Producer Edition. It is really a great DAW once you adapt to the way things are done in Sonar vs other DAWs. They have made significant improvements to their audio engine, and it runs very stable on my Q6600, 2.4 GHZ box built by Sonica Audio Labs. It is my undertanding that the downloadable free-trial version is avery much scaled down version of the full program. Sonar 8 PE includes three install dvds, so it is a significant file and cannot be downloaded.
* Hollywood Edge Sound FX library for Dimension Pro
* Z3TA+™ 1.5 waveshaping synthesizer
* Surround mixing in over 30 formats
* SurroundBridge™ technology to use stereo FX in surround
* POW-r dithering
As you can see its specifically plugins and VSTi... if you have your own, you won't miss many of these, though alot of people do like the synths. I only have Sonar 6 so I don't know about the newer stuff like Amber and the 64 plugins (besides VC), but Sonar is a great DAW that stays at or ahead of the pack and their support is great. There is no functionality differences between Studio and Producer.
Don't know if it's still like that but when i first bought sonar ( 3 ) the SE didn't have per channel eq wich was one of the major difference between the two version. I bought the PE just because of that.