After a quick peek at the data sheet for the TI chip mentioned earlier in the thread it looks like the pins 51 and 52 (voutr and voutl) on the chip are the line level outputs, a few minutes with a soldering iron should easily move the connection for the 1/8" jack from one to the other and avoid the simple onboard amp outputs 55 and 56 (hpr and hpl).

Sorry if this is redundant to something else in the thread, I was getting a bit tired of the speculation as to how the chip worked and it's ins and outs without anybody actually just taking a peak at it's block diagram.