Using the car/sled connector I haven't had any problems using a straight through cable to a PC i.e. every pin 1->1, 2->2.

I did already confirm that the sled connecter was a DCE interface and not a DTE interface like the one on the empeg itself. Perhaps you never saw that thread (don't know how you didn't though )

As for the echo, if it's uploading a kernel OK, then that really should cause problems. The fact you say intermittent reallys tends to suggest an intermittent short between TX and RX.

When it's echoing, try unplugging from the empeg so you only have the cable connected and see if you get one copy of every character typed.