On page 31 from your BD55 manual, set the Digital Audio Output to "Bitstream".
Then, set the BD-Video Secondary Audio to "Off".
From page 32, set the Analog Audio Output to "7.1ch", if your setup is a 7.1-channel configuration.
And on page 34, do the multichannel analog bass management setup,
and don't forget to click on "Complete", when done.
>>> Anytime you make a change in that section, you have to click on "Complete", each and every time, it is very important.
* I know, I also got the BD55, and used it the same way than you do.
** And do plug the eight (8) analog interconnects, with extra care, from page 12 (Connecting to 7.1ch Audio Out terminal, section E).