Thanks. The design doesn't seem to be attracting much interest though. I have a couple of other things I'm working on, a USB DDS signal generator based on an ebay AD9850 module + PIC 18F4550 and another compact headphone amp based on the AD3897. I might get on with writing them up and leave this on the back burner for a while.
The digipot is interesting, THD is not as good as the high-end TI and Cirrus chips though, but still probably below the threshold of hearing. The problem, as I see it though, is that you have to go with the uproc if you want a readout of the setting, in which case you might as well go with the high-end chips. If I could get another decimal place in the THD over the existing chips I'd go for it, because people like the margin of performance, unless they're tube enthusiasts.
I had another idea for a simplified protection circuit, I'll write it up in the AD3897 thread I'm going to start.