Stewart, Kudos! Clearly what you did was an accomplishment.
Having spent 40+ years of my career working with computers and having learned to program in several languages (over a dozen if you include things like Rexx and JCL), I now want a rest. Something simple and well documented, like an ordinary hi-fi (which some non-audiophiles, even relatives of mine, still find too complex to hook up and work themselves).
I rather agree with Brian that "the technology is [not] mature enough" for what I hope to do. There still is no simple way to make a PC into a preamp -- unless you buy, say, a Trinnov Amethyst, which for about US$10k seems to be a PC in a very pretty case with a great little display and some advanced software. But it IS a preamp, so besides DSP, it does source switching, volume control, and all those functions that seem difficult to implement on a general-purpose small computer. We are chipping away at it, but the whole picture isn't there yet.