In the end arrangers are about playing music with a backing...

You can use :
- sequencers/audio players
- arranger styles/multipads
- arpegiators
To create a backing

Espescially in the sequencer department, most arrangers are still quite basic...
Its enough for straight replaying
But its not the musical tool, more advanced sequencers offers.

Also advanced arpeggiators, could add a lot more depth..

I made an overview of most options available in hard and sotware overhere.

http://keyszone.boards.net/thread/294/backings?page=1&scrollTo=464