Only if you consider subwoofers for high-end music reproduction, I can gladly recommend REL subwoofers beginning from the Strata II. My favorite is the Stadium II. They share one thing: transparency and ability to disappear with only widening and deepening the soundstage. They match up even with electrostats in speed and definition! And they offer true linear bass extension down below 20 Hz (the Stadium II reaches 8 Hz at -3 dB in average rooms).
