We design a wooden box with a high-quality speaker inside. Inside the box we have a Raspberry Pi 2, which generates music. We need about 15 Watts power for the speaker, max. We could amplify the output of the phones jack. A better solution might be the onboard connector P5. Is there dedicated Raspberry hardware that connects with P5 and delivers enough power for "loudspeakers"?
One nice solution would be to use TDA7297 stereo amplifier IC (2x15 watt stereo), and build a custom PCB:
You can even buy an amplifier based on this IC from Amazon:
I've tested this circuit, and it works fine with RPi.
- GPIO 2 and 3 for configuration
- GPIO 28 through 31 for the sound interface
but the "older" DAC (not DAC+) on the other hand does not use any of the GPIO pins but the onboard sound connector P5. However it only works with the older Raspberry Pi models A and B - which makes me wonder why you seek to use the P5 connector with a Pi 2.
Disclaimer: I am not using any HiFiBerry boards as of now, so this answer is based on the available documentation only.