WLED has sound reactive plugins for built-in effects. Looks like there's some new stuff in .14 for this as well -- but I haven't followed closely.
Or if you wanted to externalise it completely - it supports DDP/E1.31 -- you could generate the required effect externally - and just send the commands over the network. That should do 40 updates per second for 300 pixels. Ideally send it over ethernet - but you could probably pull it off over a good wifi network.
Thanks for the pointers! After digging a bit more, I found https://github.com/scottlawsonbc/audio-reactive-led-strip which looks like an excellent end-to-end setup that's also easy to explore further from. Can't wait to sink lots of hours into it :D
Or if you wanted to externalise it completely - it supports DDP/E1.31 -- you could generate the required effect externally - and just send the commands over the network. That should do 40 updates per second for 300 pixels. Ideally send it over ethernet - but you could probably pull it off over a good wifi network.