DSD is not just PCM @ 2.8224 MHz/1 bit (or however you like to think of it). Think about what it would take to convert DXD to DSD (DXD was supposed to be a higher-grade format that downconverted easily to both DSD and PCM).
EDIT: And if you doubt, answer this question: why can't one convert an optimal square wave in PCM (I.E. 0-0-0-...-0-2^16-2^16-2^16-...-2^16-0-0-0-...) losslessly to DSD and back to PCM? (And substitute in for "2^16" whatever the equivalent equivalent amplitude is that DSD can handle [i.E. if DSD is "equivalent" to 10 bits PCM, then 2^10].)
You are correct in terms of delta-sigma DACs, though.