This is a basic microphone and pickup setup that generally works well on the Ark's Yamaha grand. Feel free to try out other techniques, but this is a good starting point.
The setup uses two microphones, in this case the AKG-460 mics. It also uses the Barcus-Berry pickup system which is mounted on the bottom of the piano, near the tail. The mics and the pickup all need phantom power.
The two microphones are placed above the strings, pointing straight down. Distance from the strings should usually be between 1 and 6 inches. Closer reduces bleed and feedback, but doesn't sound as good as farther away.
Little or no EQ should be needed. The really useful thing to do is to set the channel low-cut filters. For the pickup, around 50-100 Hz. For the mic on the bass strings, 100-200 Hz. For the mic on the treble strings, at least 200 Hz. This will cut down on low-frequency feedback quite a bit.
The mics and pickup can be mixed with roughly the same input gain and fader position, at least as a starting point. Since this piano is rather bright, the treble mic may need to be mixed a bit quieter depending on how hard the pianist plays.
The pickup is used to add "body" to the sound. By themselves, the microphones will tend to give a rather bright, string-heavy sound. Mixing in the pickup fills it out, and since the pickup is resistant to feedback it also allows more volume before feedback. The pickup can also be used as the main piano feed to the monitor mixes, since the performers on stage will be close enough to hear the strings directly.
Low-frequency feedback problems can sometimes be fixed by changing the polarity (aka "phase") on all of the piano channels. Also, the folding plexiglass screen can be placed between the piano and a drumkit to reduce bleed into the piano mics.
This is the usual Barcus-Berry 4000XL piano pickup system. This system includes a piezo pickup and a DI/preamp. The pickup is good, but the preamp box isn't a good match for it. Some piezo pickups require a very high input impedance to sound good. That's the case with the Barcus-Berry pickup. However, the preamp only has an input impedance of 2.2M. I discovered that modifying the Barcus-Berry preamp for a higher input impedance (I used 10M) improves the pickup sound dramatically. An alternative to modifying the preamp would be to replace it with a high impedance DI such as the Baggs Para-Acoustic.