Room acoustics - finished or unfinished wood

I have a 25 ft by 16 ft listening room with 9 1/2 foot ceilings, with exposed spruce joists running parallel to the short wall...7.5 inches deep and about 14" between each pair. My painter, also an audiophile, recommends following a coat of stain with a coat of polyurethane sealer. The question is basic, will unsealed wood better attenuate the high frequencies than wood sealed with polyurethane (flat)? The room probably needs some high frequency attenuation, given wood floors, etc.