Something that doesn't respond all the way to 20Hz. Demo some floorstanders that respond to 35-40Hz on paper allong with a pair of bookshelf speakers that respond to 40Hz. A good floorstander should respond evenly down to this range without getting into the super low frequencys. There are some quality bookshelf speakers that are remarkably close to full range. I don't know what your pre/amp combo is but the Spendor S6 or S8 comes to mind.
Good luck!
Good luck!