I own LASS 2, East West Hollywood Strings Gold,EWQLSO Gold, 8Dio Aggitato series, Symphony Strings Essentials (came with K11U), some solo strings from Embertone and Albion/Albion One from Spitfire.
I totally disagree with some of the over the top comments that this library is half-assed etc.. Come on really? Audiobro makes great stuff, including this one. I also disagree that it can't sound organic! Nonsense! It lacks articulations from the full version but still useful. Whether its price is competitive anymore with the explosion of newer string products that have been released since it came out is another story. Using Virtual strings is all about learning the library in and out and getting the most out of it and not expecting it to knock your socks off when you play a note. It's nice when that happens but even libraries that do that will be limited in other ways.
To answer your question about upgrading to K11, since K11 does not contain Symphony String Essentials then you can't update it to the full version since there is nothing to update from. You might be able to "crossgrade" but I didn't see that as an option on the NI website so you should contact NI first just to make sure.
Now after defending SSE from some pretty ridiculously harsh comments (sorry guys, but they were) I would say that if your main purpose is to get a good string library that can do way more arts and probably more expressive sounding then for just over $300 you could grab 8dio's Century Strings which is 40% off right now and I think is money better spent if your main goal is to get a good String Library. Also the new Chris Hein Ensemble Strings. Both of these seem to be taking Strings to another level when it comes to the ability to be more flexible with your string writing. There are many great libraries out there in the $400 price range today that makes it harder to recommend one over the other but the two I mentioned seem to offer something beyond just being another String Library. Having said that the Divisi feature of full version of Symphony Strings is one of its strong points that the essentials version won't give you and something that Audiobro is known for. It seems to be an easier way to do divisi over what LASS 2 can do. Here's hoping to LASS 3 soon
In the end just learn what you end up with in and out and you'll make great music. In the $400 price range there is a lot of good stuff out there.
In regards to Symphobia, it's apples and Oranges. Symphobia contains ensembles with Brass and drums and woodwinds and choirs etc.. and won't do as detailed for strings but still sounds gorgeous.
We're spoiled for choice today but don't let anyone make you think that you can't write professional score's with Symphony Strings. There are well respected composers still using parts of EWQLSO to this day in their compositions. In the end it is still about learning the VI's you have to get the most out of them.
What I think you should consider is where do you want to start? If you're doing just trailer music and not a lot of detailed writing then jumping to Komplete 11 Ultimate is possibly a better way to go. You'll get all the Symphonic Essentials but also so much more that will help with trailers such as Damage, Evolve, some great pianos, drums, bass,Action Strikes, some great synths , and so much more.
Back to Symphony Essentials -Just for comparison sake, here is a nice little video comparing String Essentials to Spitfire Symphonic Strings. You might be surprised at how well the sound stacks up to a much more expensive Library. I love Spitfire but I do feel they are over-hyped on this forum. There was a time where saying that might have even got me banned around here
- but don't let anyone make you think you have to own Spitfire to be a competitive composer. Just buy it if you like it.