Hi Steven,
somehow I don't understand the wiring you proposed to use. I tought I would have to desolder R756, R757 and R754 in order to boot from sd3....?
hdparm -S 120 /dev/sd[bcd]opkg install xbmc_13.beta1.04-imx-r1579e85d88-1_armv7.opkmount.cifs //matrixtv/root my_mountpoint -o username=root