How Do You Record Your Acoustic Piano?

Hispringgrass , i can address this immediately: for the greatest dynamic range you ideally use microphones with very low self noise so that the most silent parts can still be caught in all their detail. The preamp gain would be set while playing the loudest parts to a level so that the signal would not clip or distort. That said if you don't go too far into the room most of the usual condenser candidates should be sufficient but at least for the room mics extra low self noise would greatly benefit the recording in the ppp parts.

Make sure your A/D supports at least 24bit resolution, if possible even go 32bit. This exceeds CD standard but is supported with high end streaming providers such as Tidal, Apple Music and others. 

Of course you also need to pick a piano that can take fff without choking and also a room with very low self noise. The ideal space is quiet and resonant, but also well-controlled with a reverb time between 1.2 and 1.8 seconds and a balanced frequency response.

However when listening back such recordings on your stereo at home with 1:1 dynamics this would most likely be too silent in the silent parts and you'd blow away yourself and your neighbors if you reproduce the fff of a concert grand in your living room (besides that you'd need exceptionally capable speakers) so volume riding the faders slightly and/or even compression would most likely be applied during mixing and / or mastering stage. I'd recommend a combination of parallel compression with slight psychoacoustic eqing to bring up the silent parts - and a slight soft knee compression to control only the utmost excessive peaks.

Difference sad vs happy piece:

If you have the possibility to choose between instruments and room you might choose a darker timbre for a sad piece and a silent but more resonant room. Apart from that use closer main miking for more intimacy (above the soundboard) but also far room mics for depth and blend to taste during mixdown (room not too dominant). If you can't choose the instrument you might slightly boost mids and low-mids to help with "warmth" for the sad piece, treble not too shiny. 

With the happy piece the room can be more lively though potentially with shorter reverberation time. If both needs to be recorded in the same room you could bring down reverberation with absorbers (even sheets) yet mix in the room a tad louder. Increased main mic distance as compared to the sad piece, most likely in front of the piano - this picks up more room already and sounds less intimate but more open and lively. Choose brighter instrument or slightly boost high mids and treble as compared to the sad piece to help with brilliance and energy. 

Most likely i don't need to tell you but:

Sad doesn’t necessarily mean quiet, and “happy” doesn’t automatically mean loud. It’s really about the tone, the space, and all the little nuances that carry the feeling. The way you mic the piano can help bring that mood out. The tech would be following what the music wants. 

In a way, you could even say there’s no fundamental difference in approach between a sad and a happy piece. You move through the room with your own ears, listening closely to how it sounds in different spots. The sound changes every few inches, and there are a few sweet spots where it comes across especially detailed, balanced, deep, spacious, dark, bright, and so on.
Once you know what the music wants, you’ll naturally end up in positions that roughly match the qualities described. But in both cases, your approach is the same: you’ve listened carefully to how it sounds where, and based on that, you decide about mic placement. 

However, even the best ears in the room can’t perfectly judge what the microphones are actually capturing, as a mic has its own directional pattern and tonal response. So what sounds perfect to your ears in the space might not translate the same way to the recording.

So the “royal road” would a combination: use your ears to find general sweet spots and musical nuances, then fine-tune the mic placement from the control room. Via talkback, a colleague can adjust the microphones while you hear exactly how each position translates to the recording. This way, you capture both the emotional intention and the exact sound the microphones pick up.

Wow this became way longer than i thought. Maybe you're all helping me write a little book someday ;) So thank you for that inspiration :)

Rainer Joos said:
A practical approach, if experimenting: try a small tilt of about 5–10° towards the soundboard and critically compare the result.

I did just that and as a result this is how I place the microphones, together with boom like positioning of the microphones on order to have no lid reflection at all. I will try EBS tomorrow on the D and the 225 Bösi and report progress. I like NOS because of its sound, naturally, but also because of its simplicity to set up, because a regular volume of classical sheet music gives you both ~31cm and 90° angle :-)