dmw,
Lots of good advice from Bren, Ajax and all, but a mix of both reflective and absorbent surfaces is ideal. Axiom speakers are designed with consistent frequency responses both on and off-axis such that early and later lateral reflections from side walls will add to the sense of spaciousness. That has been confirmed by many tests at the NRC in Canada.
So normal domestic furnishings--upholstered furniture, area rugs, some bare walls broken up by bookshelves, etc. You don't want the room excessively "live" or "dead".
Regards,
