I do not use it for any DSP, but R does have signal processing packages available. And it is free and multi-platform.
Edit: I love this topic. Subscribed.
So it looks like I will be getting an office in the next few months which will become home for the Oppo HA-2. It is now serving the duty of the DAC in the home headphone rig and will thus need to be replaced. If anyone has, or knows of, a Yggdrasil for sale, please let me know.