I don't really think you get much out of those arm chips that you don't out of the 8-bit chips, for what you do.
Audio is very slow (for mcus), other than fft and potentially graphics. If it is simple controling of a relay, or a digital pot, or bias adjustment, or speaker protection, etc. your 8-bit mcus, especially multiple of them each dedicated to a particular job, would be a more efficient way to go.
Having said that, the arm chips offer a lot of value. I have no problem what soever with CoIDE (a big fan) on STM32 and older Luminary chips. The issue of limited device support, as mentioned earlier, is true, only if the device you intend to use isn't supported.
I would also recommend TI's ARM chips particularly their launchpads - incredible value for a feature rich chip. The free version of ide (CCS) is fully functional as well.
I am also a big fan of PIC24 chips and think they offer a lot for such a little known chip. You do, however, have to pay for the compiler for a fully functional / uncrippled version.