Based on the comment below on your rca, u may consider to replace your rca before adding extra stuff, since your speaker should not perform what you missed (see second link for comments on your speakers): http://www.musicdirect.com/p-290-audioquest-sub-3.aspx
i think marantz + atohm will not give you burr sound of piano.
try the thing cost nothing first such as speaker position.
then may be you can change the speaker cable and interconnector.
try belden or mogami - cheap cable which has no sugar first and see the effect. they only cost you less than a thousand dollars.