I have an S550 as well (soon to be 2 of them...Both models can be made region free in seconds with a few button pushes on the remote...The big thing so far for me has been the mpeg4 playback...
Odds are that file will at least get you the majority of your basic functions...But only missing "on screen" button/code for this device...View topic - YamahaDVD-S550 the "on screen" code...
www.itepe.net/]LINK[\URL] CP1250 s550 v.10i (24.12.2005) with good results - no packed bitstream problems anymore, ID3 tag, long filename and easy directory browsing for MP3/DivX on TV display...mtz.softpedia.com/index.php?option=com_content&task=view&id=20&Itemid=2]LINK[\URL] - that looks wayyy too fiddly (hesitating to make up a serial cable though until I know that I need to for...