* with all the instructions/examples I finally managed to produce 480x272 logo bin files that can be loaded and modified by GIR_Editor. I actually created two versions: one with a single image, and the other with 2 images. Both can be loaded onto the 660, and both showed the correct boot-up image.
* What I did was simply putting the header and the bmp(s) together, filled it up with FF, and with a dummy checksum byte; the I loaded into GIR_Editor, replaced the image, and saved -- the tool will produce the right checksum.
* However, It now seems that there are two display steps , one for boot-up, and one for initialization and USB connection mode. The first one is now all correct. But the second one is still messed up -- It looks like that every line gets left shifted by a pixel or two compared with the previous line. With the 2 image version (both images the same) the second display also has a very dark blue overlay (the twisted imaged was barely visible). This looks like it is trying to display a e.g. 478x272 image into 480x272; each line eats a couple more pixels from the next line the the previous line.
* Moreover, with the single image version, I can change the splash image via the "display" setting (previously frozen); it works, but again, only the first display is good; the second one is the shifted/twisted version of the first one. With the two image version, this would freeze as before.
* So it seems that a single image is correct (no freeze, replaceable); however it seems that the logo bin file needs some extra information, probably at the end of the image file (I think my 2-image version was not right, but the bytes after the image made some difference).
* The problem of GIR_Editor with the "original" logo.bin was the incorrect size of the bmp (the header has the right size which is 480x272x2, but the image seems larger). But that one (despite garbled) shows up the same way for both display steps. So there is something right about the "wrong" size ...