Hello Magister85,
1) 8 gb ram notebook
2) Samples hinsz Kampen vol 2 (I use it with the truncation of the reverb)
Assuming that the notebook has sufficient processing power, and meets our perquisites, then that sounds fine.
The MDA Hinsz Bovenkerk Kampen Volume 2 sample set should easily be able to load within 8 GB of physical memory in 16-bit (compressed).
The sample set is quite 'wet', and truncated releases can only partly make a wet sample set seem 'drier' (for example, because the real organ's acoustic will have been recorded into the attack/sustain portions of the samples as well as the releases). Hence my personal preference for use within a reverberant space might be to go for a sample set that's naturally fairly dry (or 'semi-dry'), but if the Hinsz sounds good with truncated releases within your particular building, then that's fine.
4) RME Fireface UC suond multichannel card usb
That isn't an audio interface that we've tested or have any feedback on, but RME's products are usually excellent, so I wouldn't anticipate any problems there.
3) Def Tech SuperCube 1 (I can not tell if the church or should I just buy a bigger one. The thing that puzzles me is that if you increase the volume beyond the 25% you feel very bad sound)
...
5) Two Mackie 824 mk2 active monitors.
I'm not an expert on speakers, so I'll leave other forum members to comment on those, although I understand that they're highly-regarded speakers amongst Hauptwerk users.
Perhaps if you give some more details on the building (size, reverb time, shape, etc.) people will be better able to make useful suggestions.
My general suggestion would be that I would guess that you might need more than a single pair of speakers for a building of moderate size or larger. More speakers also allow you to use multi-channel audio, distributing the virtual pipework around within the real building and thus making it appear to fit more more naturally into the natural acoustic of the room.
With just a single pair of speakers all of the pipe sound will appear to emanate from a single point in space, whereas each pipe in a real pipe organ speaks from a slightly different point in space, giving it perceived clarity, separation and direction. Using more speakers gets closer to that.
Hope that helps to some degree.
Best regards, Martin.
Hauptwerk software designer/developer, Milan Digital Audio.