(To throw in a different take). I definitely like C++ more for ease of interface.  Templated math functions and overloaded operators are just too nice, the code looks so much better (at a user level).

There are also plenty of audio languages written in C++ - SuperCollider, ZenGarden (which is coincidentally a rewrite of pd-core in C++), and Faust are the first three that come to mind.  For graphics, there is both openFrameworks and Cinder, which each use very different features of the language.

In the end, I think you should use the language with the features you wish to use.  While you could build an OO language on top of C, it is essentially a procedural language, so why bother when that is what C++ is for?