As far as I can tell, if you get the extended version(600 dollars more) it has some extra instruments taken from their newer libraries(Harpsichord, Organ, Electric and acoustic guitar, piano) and a few other things that Opus 1+2 does not have.
Since the performance tool is integrated into the Kontakt version of Opus that's not something which necessarily sets the VI libraries apart from the VSL Horizon series. Furthermore the Special Edition lacks some articulations and in some cases also some velocity layers compared to Opus. There is no convolution reverb in SE like there is in Kontakt/Gigastudio so if one does not already own one one might need to invest in this. You can only run SE on one computer whereas you can run Opus on multiple ones.
On the positive side it seems to be very easy to set up articulation switching/layering/crossfading the way you want it with SE, although one might not benefit from this as much as with other VI instruments with more articulations to switch between. SE also has 24-bit samples and more instruments than Opus and thanks to the real-time decompression the RAM usage for the 24-bit samples is lowered. There is no upgrade path from SE to the cube, although the possibility of future add-on packs was mentioned on the VSL forum. I hope this helps.
That's some interesting information. Also - the fact that there IS an upgrade path from Opus to the cube may make it more practicle, certainly since I already own kontakt. If the performance tool issues are kind of solved in Kontakt that could be a good way to go. I think it looks like Opus has more articulations (which is why I'm inquiring about all this) and I actually tend to like the Opus demos better than the SI ones, but that could be perception.
The SE DOES have the appassionata strings - which I know Opus doesn't have - and Opus doesn't have the solo or chamber strings - so that could be a plus to the SE version.
I'm a very proud opus user but will probably not be upgrading to SE anytime soon. Even with the new instruments, I personally cannot justify the upgrade cost vs what I already have in Opus.
Judging from the articulations list, we have a more complete product in Opus 1 + 2 in terms of depth of articulations, runs/trills, velocity layers, alternations, etc, but SE obviously has the edge in the sheer amount of instruments! However, upon closer inspection, beyond the Chamber and Appassionata strings (I already own Horizon solo strings), epic horns, and the occasional use of Saxophone/Eb alto clarinet/Wagner tuba for wind symphony pieces, I cant see myself using many of the new instruments. I guess they're nice to have "just incase," but I personally would have liked to have seen more articulations for the common instruments vs more exotic and rarely used instruments. I mean, I imagine I'd use trills or runs far more than I'd use the Oboe d'amore or Basset horn instruments. I'd also imagine I'm not in the minority here.
Also, SE has less alternations/velocity layers in comparison to Opus, and I wonder if this will make it hard to do mockups? Some patches only have 2 velocity layers and no alternations! Jays demos sound GREAT, but they are legato heavy. I'm still waiting for VSL to produce an "action/repitition heavy" demo for SE before I judge, but thus its another reason I will not upgrade to SE yet.
Here is my unofficial list of NEW SE instruments not in Opus 1+2 bundle:
Solo strings (available in Opus 2, but no legato?)
Small clarinet in Eb
Epic Horns (available in Opus 2, but no legato?)
Electric guitar, distorted
Note, if you dont get opus 2, you dont have muted brass & woodwind ensembles or the demo patches for Solo strings and epic horns.
Though Opus is missing some instruments that maybe nice to have in SE, the amount of articulations/alternations and velocity layers of common orchestral instruments makes up for this in a BIG way imo. But remember, I dont have SE to compare, so YMMV, but I am extremely happy with Opus! If you'd like, I can post some demos later in the week of my current work that uses 99% VSL Opus. Let me know.
I dont have a full list, but a typical example is the staccato patches for any woodwind/brass. Opus usually has 5 dynamic layers, where as SE only has 3. This in particular worries me, as I use different velocity layers to avoid the "machine gun effect," in which its very helpful to not only have 2 different staccato patches, but also more velocity layers.
I can search for more examples if you wish, but this is the one in particular that has me worried for ostinato type writing. Perhaps I'm nitpicking though? Maybe realistic repetition can be achieved with only 3 dynamic layers and 2 alternations?
Some examples of missing articulations in SE vs Opus that I personally would miss (in addition to the trill patches mentioned before) are col lengo (the bow against wood sound ala Holst's Mars), flutando (flute like strings GREAT for ambience in film scores), sordino (muted strings; works great behind dialogue in film scores), etc. I've even used things like flutter tongue for the flutes and trombone slides in past works which sounded GREAT! All these are not available in SE, which is a real shame. Thus my comments that I would have rather seen a more complete VI "orchestra" rather than all the addition "extra" instruments.
There have been comments by herb at VSL (owner) that they may develop "expansion packs" for SE, but this was just an idea and who knows if it will be implemented. I for one REALLY hope they do, seeing as how you have no upgrade path for SE.
I just received my VSE VI yesterday and I friggin' love it. I'm actually digging the Extended library as part of the 30 licence you get when you buy the library (NOTE- the 4 DVD set comes with the extended library and is unlocked with a license. Good idea on the part of VSL especially since I'm really loving the extended instruments and figure I'll have to fork over the extra cash to keep them after the 30 trial is up!)