Hi, actually DigitalReadSerial is not a command but is a sketch, that is under the Examples 01.digital menu
The speaker is hooked up through a 4.66k resistor connected up to a transistor, that then feeds speaker. The other side of speaker has +5v going through a 50ohm resistor and, there is a diode... There is a schematic of an earlier version of this shield up on my thread at: http://www.lynxmotion.net/viewtopic.php?f=26&t=8021
I am including a zip file created of my main test program. It is not great, but does allow me to check out different things of my shield. There are hacks in place as not everything is ported. Also it has a PS2 (playstation 2 test), that relies on a PS2 library, which I think I have working port of it. It is up on my github account github\kurte
I am trying a couple of different things to see if it works. Like I took an unpopulated shield, put it over the DUE and use some spare stackable headers, which I know won't make great contact... I then put in the three buttons, again no solder. I tried the digitalReadSerail sketch and at least 2 of these worked then. So on my populated version I have removed the PU resistors to see if that helps... Nope...
Kurt