i never tried to run my hdsp with oss ... have you tried wini's asiomm or jack?
jack works, but gives worse latency, and the need for realtime modules to make it run as non-root user. i haven't managed to get wini's native alsa support to work, is it true that it is merged into miller's 0.38 branch? It's no big problem, since i can get pd to run with hdsp multichannels either way, just thought it was an interesting fact.
cheerio says.. Peter