I went to the Intel site and see a memory spec for core i7-900 seires cpus supporting a memory type of ddr3 800/1066. However the motherboard for those cpu, the DX58SO, specs DDR3 up to 1600mhz.
Is there an answer to this apparent conflict in the specs for the cpus and the associated motherboard?
It just means that the motherboard can support ddr3 memory modules up to 1600 mhz. Most 1366 motherboards support those speeds.
Just remember that the i7 9xx series changes your memory frequency to 1066 at stock.