You guys are worth your weight in gold.
Will:
Replacing -rt 90 with -ls did the trick.
After much trial & error, I guess the default fit width is the best bet. Using this, sometimes the diagrams get cut off, but its the best option for text (that's what books are for, right?). I tried to play around with the grid option, it is good for the diagrams, but not so for the continuity of text. With/without specifying the output size for my M96, & due in part to the inefficiently/over-zealously cropped margins in briss, I think it struggles to fill the pages with the available content & leaves empty space at the bottom of the page (if viewed in output landscape mode). Just not worth the trouble. I'll just leave the thinking to k2pdfopt.
Mark:
M96 software is still a work in progress. Its default reader allows full screen landscape mode but has a lot of lags (5-10 seconds or more) while switching pages even in the latest software version, & sometimes garbles/eats up page contents altogether. Other apps like ezPDF are better, but then they don't turn pages with buttons/d-pad in landscape & need to move the page with stylus, or need elaborate workarounds like a precise zoom, assigning volume keys for page flip & then work perfectly. Phew!
All-in-all I guess conversion to landscape using k2pdf & then asking M96's native viewer to treat it as normal portrait is the most efficient compromise.
Jp