Yeah Stephane, putting either the speakers or your ears very close to the wall behind them increases the bass. From your measurements, it appears that the back of the speakers were already only about 13" from the wall, but since there're no rear ports, have you tried putting them just an inch from the wall to see if that similarly increases the bass, but with a closer sitting position?
As to a separate DAC, it's unclear how anyone can "hear" how one sounds independent of everything else. An audibly significant difference due to that alone is highly unlikely these days.
