Media Center HD recording issue

Media center records fine except on HD channels where I think the data rate overwhelms the system. Unfortunately media center defaults to recording HD if it can. Is there anywhere to globally change all recordings to to SD rather than HD ?

I can't find anything that is global. The best I've been able to find is the Series Settings, which can be set to SD only. Probably can fix this with a registry or dll hack, though you aren't likely to find an enthusiast busy hacking to downgrade the default quality :)