some ideas and targets here.

libpsynth: This is a powerful C++ library for the building of synthesis software. It provides, among other things: abstraction over the audio devices of the system, basic audio synthesis classes (oscillators, filters, etc.), a system of connectable synthesis modules with a generic API, classes for the development of interactive synthesizers with features such as automatic module linking, MVC and facade layers, classes for the synchronization of synths over the network using OSC, a framework for easy application creation, etcetera.

so much good stuff here, mml loader, multichannel synth (with well thought out api). So worth borrowing.

arduino based SID emulator

various synthesizer kits. Some very interesting things here, including modules, and full on, midi controlled, VA avr based synths. Also, they sell boxes.

some moog vids