that's just more acceptance filters. First you set up IDAM bits and choose between two 32bit filters, 4x 16bit filters, or 8x 8bit filters. Each filter can accept and pass some messages.
In 32bit acceptance filters mode, one 32bit filter is using acceptance registers CANIDAR0,1,2,3 and mask registers CANIDAM0,1,2,3. Another 32bit filter is using CANIDAR4,5,6,7 and CANIDAM4,5,6,7 respectivly.
In 16bit mode there are four filters:
CANIDAR0-1
CANIDAM0-1
CANIDAR2-3
CANIDAM2-3
CANIDAR4-5
CANIDAM4-5
CANIDAR6-7
CANIDAM6-7
In 8bit acceptance filters mode it's strightforward x-th filter is using CANIDARx and CANIDAMx.
If you need just one filter, then just setup both "banks" the same.