The good news is that VSL has taken everything off your hands to record the grand piano of your choice in the best possible quality (mastered so to say).
Furthermore, VSL provides you with various presets to choose the sound you like best with your piano.
Since you don't have an orchestra or other instruments, you don't have to adjust the grand piano sound to those other instruments. Easy!

Then it's just a matter of A) finding the right volume, B) possibly limiting the dynamics a bit and C) possibly optimizing the overall sound a bit (adapting it to your taste).
A) may depend on whether your music is in competition with other pieces - maybe even from other competitors...? Or it depends on how you want to publish your music.

B) C) are, as I said, just a matter of taste. B) for a solo piano without other instruments, the dynamics may remain uncompressed. If you want your music to be heard while driving a car or listening it in a train, I would increase the quiet tones a bit (NewYork compression).
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So what could mastering mean in your case?
Perhaps it would make sense to look for piano music that you particularly like in sound. Then "mastering" could mean getting as close as possible to this reference (sonically speaking).  
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Then there is a so-called technical mastering. This involves making sure your music files are technically OK. Remove rumble, channel balance OK, remove unwanted noise, pause about 2 seconds before the music starts, make the file length so that the fade out is not cut off, max amplitude about -0.7dB... such things...

Beat

Originally Posted by: Cyril Blanc

...Do you also have recommendation when you mix a full orchestra using MIR PRO 3D

Best Regards

Cyril

Hello Cyril
While "mastering" used to be necessary in record times, mainly to comply with physical necessities so that the pickup needle did not fly out of the groove or get too hot, mastering today usually has a different task.
In some music genres it's about giving music enough volume and power, in other genres it's more about getting the last bit of quality out. The latter is probably more true for classically oriented or film music. Also, the line between mixing and mastering is not so clear-cut.

As I mentioned above, the technical mastering - that is, that a track is audio-technically in order and also in the desired format - can be done well by yourself if you have the appropriate software.
The audio fine-tuning is on the one hand a question of taste, or the perfect approach to a reference, as mentioned above. If it is only a matter of fine tuning, then the mix should already be perfect on the one hand, and of course also the monitoring system, so that the right decisions can be made.

So for the hobby sample mixer, "self-mastering" could mean getting as close as possible to the sound of a reference with real recordings that are relatively similar to your own music.
Switching back and forth between one's own mix and the reference, one notices relatively quickly whether one has achieved a similar sound, or whether one is perhaps even completely off the mark.
I can only recommend this step of comparison to every "mixer", because one of the main mistakes of many hobby mixers is that they turn the "knobs" of the effects too much and often too strongly, although the sample manufacturers actually make a lot of effort to offer a good sound by default.
This "turning of the knobs" usually results in even more "turning of the knobs" elsewhere. So mixes can get completely out of hand without you noticing. The above-mentioned comparison then quickly shows whether you are on the right track or whether you should perhaps start again from scratch with the mix. This recipe applies whether you work without or with MIR. Even with MIR and its many setting options, you can still end up on the wrong side. Comparison shows it!

So the track is not yet mastered but at least well mixed and thus a good starting point for further optimization - if desired..

Beat

Originally Posted by: Cyril Blanc

Hello Beat,

Many thanks for your answer.

What do you think of my idea of mixing a song with a full VSL VI orchestra + drums and singers.

I mix using MIR PRO 3 D
I set the volume at 0db in MIR 

Each desk is send to a separate bus 

I mix each desk separately in Logic
If I do not use a VSL instrument I use Logic's EQ and Compressor
Then I mix the desk all together 
Do you mix with earphones ?

Best

Cyril

Hello Cyril

It does not matter how you arrive at a final result. It is always the result that counts.

A) For larger projects it makes sense to know from the very beginning where on the virtual stage individual sections will play. Create a sketch and try to reach the planed positions acoustically

B) So that everything plays under one roof in the end, I would personally only work with room depths during the entire mixes and always switch off the reverb tails everywhere.
Only during the big mix of all tracks and stems would I put a single tail over everything - just as you want it.
This helps to glue all the individual mixes together.
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I do a lot of work in the headset. All the positioning of instruments (the implementation of the stage plan) and the final mix I usually do through the monitors. This gives me more reliable results than using the headphones.
Of course, you need a good monitoring situation to be able to work in this way.

Beat

Originally Posted by: Beat Kaufmann

Hello Cyril

It does not matter how you arrive at a final result. It is always the result that counts.

A) For larger projects it makes sense to know from the very beginning where on the virtual stage individual sections will play. Create a sketch and try to reach the planed positions acoustically

B) So that everything plays under one roof in the end, I would personally only work with room depths during the entire mixes and always switch off the reverb tails everywhere.
Only during the big mix of all tracks and stems would I put a single tail over everything - just as you want it.
This helps to glue all the individual mixes together.
------------------------------------------

I do a lot of work in the headset. All the positioning of instruments (the implementation of the stage plan) and the final mix I usually do through the monitors. This gives me more reliable results than using the headphones.
Of course, you need a good monitoring situation to be able to work in this way.

Beat

Hello Beat,

Thanks for your answer

I am a bit lost with your answer ; MIR PRO does the room placement and the reverb of each instruments ; Don't you use MIR PRO ?

Best Regards

Cyril