its propietary, but kinda linnux inspired.
it is threaded though.
I would guess its built on top of some blackfin SDK.
I’ve done a project or two on those babies back then, and Analog Devices supplies tons of SDKs and engineer-to-engineer-notes.
But the Roku forum is more suited for that.
This could turn out rather simply, with the filter coefficients entered through the remote, or a simple-web-screen.
You would, of course, have to compute the coeffs yourself.