Hi Sheldon,
I'm not sure but I think there might be some confusion going on here.
Neither SHIFTIN/SHIFTOUT nor the MSSP module will be able to handle dual or quad SPI interface - period.
If you're going to do it you'll have to bitbang it yourself which, again, is probably slower than doing it "normaly" with the MSSP module.

The thing with dual and quad SPI is that it's getting closer to a parallell bus. With dual SPI there are two datalines and with quad SPI there are four (instead of one) that get sampled on the active edge of the clock. SHIFTIN/SHIFTOUT doesn't support it and the MSSP module only have one data line input so it's impossible.

/Henrik.