After upgrading to N6.1 now I purchased Acoustic Guitar Expansion and Mandolin Expansion set.
I double clicked each of the two .prox files to get them installed by Notion. But I didn't found them under Notion Instruments when I opened the program (Mandolin tab was still grey). I double checked the location of Sounds folder, which has the structure [Sounds/Bundled] while the all expansion sounds seems to appear straight into root of [Sounds]. Still no Mandolin and expanded Acoustic Guitar.
For the sake of experiment I even tried to made a folder containing the single MandolinExpansion.prox only, guessing, that Notion should show up that single Mandolin under the Notion Instruments and "losing" all the others, after I'll save that path under Preferences/Audio/SamplesFolder. What happened = no instruments at all (as expected) and no Mandolin at all (despite my expectations).
Is is something wrong with me or with Notion? Now I'm stuck and cannot go on with the production the way I wanted to do.
I'm on Windows 7 64bit. Would appreciate any clue.