Hi,
Basically what I was referring to using biab backing tracks with my arranger, was to load the backing tracks in as mp3's.

For home use ( which is all I do)I did actually have biab midied directly to my pa3x. Ie. Biab puts out it's chord changes over midi, I had my keyboard in arranger mode, which left me free to play melody, also gave me access to the sts's on the keyboard. Hope I kept a note on my midi setup, it wAs at least a couple years ago and my memory isn't that great.
I've also had a mix of biab audio tracks and keyboard tracks. Did it thru real band sequencer. Ie I loaded my pa3x midifile into realband, can't remember if I had to put the chords in manually, then replaced just say the drum track or guitar track with a biab audio track. The chords in realband automatically generate the correct backing. Probably not necessary on a pa3x midifile, but a midifile crested from a converted style can usually do with a bit of help.