I wrote some firmware this morning for the 1704, it uses a fixed-length loop that gets the clock in the ballpark (359.2 kHz, says the scope) if not as accurate as the 1501 with its NCO. Like the 1501 firmware, it also does 2x oversampling and has a LUT in case some manner of compensation is necessary for the internal op amps - plus it supports stereo and can probably work unmodified on the 1703, the 1704's smaller sibling that cuts out some unneeded hardware. It'd be really cool to get this to be a workable one-chip solution, with only external passives and connectors necessary.