Semi-intelligent audio system

[Styku]

Hello,

I'm planning on making complete audio system that uses RPi as a brain. I've already made an amp on TDA1554 to make volume reasonable.

Here's a brief list on what I want it to do (in order of implementation)
1. Turn on/off TDA 1554 directly from software.
2. Sleep mode, and preferably some physical buttons to set it.
3. Playing from jack/minijack input
4. Playing streams from internet radio or services like spotify.
5. Verbal interface

I would appreciate any clues on how to do it efficiently. Any libraries, APIs techniques that can be used to make it work are all welcome. Just one thing - I do prefer C/C++ over any other languages commonly used to handle GPIO pins on Pi.

My personal thoughts, correct me if I'm wrong, please:
ad. 1: Can't be to hard - a common transistor between +12VDC and amp and controlled by Pi should suffice
ad. 2: Also not a problem here, <time.h> is all I need I guess. But how to set it with as little physical interface as possible, I do not know. Maybe potentiometer (for setting approximate number of minutes) with ADC and a button to turn it on?
ad. 3: The only thing I can think of is a mixer between Pi and amp, but then the input won't be controlled by RPi (no equalization or control whatsoever)
ad. 4: Well, that's a software thing and I guess I will manage to get it done. But I will gladly accept any libraries recommendations.
ad. 5: I know how to write the ANN for this and how to parse audio input for voice features, but... How should I input audio to the Pi? Is there any other way than external USB soundcard? Or can I use GPIO w/ ADC for this? (preferably, as I want to use as little external devices as possible)

Thanks in advance for any thoughts on this topic!

[GTR2Fan]

It would make more sense to use the TDA1554's standby pin to control it in my opinion. Check the datasheet, but if memory serves it's pin 14.

[Styku]

That's what I meant - to wake it from standby/mute state I need to supply >6.4V if I remember correctly, which Pi alone can't provide. So a transistor between PSU and pin 14 is what I want to do, sorry for not clarifying that.