Toastman is merging TC-ATM patch with his code now, I think the latest version has it.
Use tc-atm setting (40bytes for me) for adsl/adsl2+ connections.
Cable and vdsl should not need this setting.
40-PPPoE LLC/Snap. I came to the same conclusion after picking through the settings/configuration on the modem.
I am still having problems getting it dialed in. Can you provide some screenshots of your current QoS setup? I have the newest version of Shibby build and it does have the "global maximum" for inbound QoS.