Zuio,
With Vandersteen, theres no question that a sweet spot will definitely be a factor. Not only off axis, but height, as well (thats why you set the back tilt). They don't sound bad if you are not in your listening chair, but you may want to consider something else if you will not always be in a listening chair.
Also, your comment about Ncore being a good match for warm speakers is relevant. If you do consider Vandersteen, that probably would not be a very good match. Its not a warm speaker. I find them to be fairly neutral and revealing.
With Vandersteen, theres no question that a sweet spot will definitely be a factor. Not only off axis, but height, as well (thats why you set the back tilt). They don't sound bad if you are not in your listening chair, but you may want to consider something else if you will not always be in a listening chair.
Also, your comment about Ncore being a good match for warm speakers is relevant. If you do consider Vandersteen, that probably would not be a very good match. Its not a warm speaker. I find them to be fairly neutral and revealing.