Ha! Now I want to try speakers tap again . I need to stop reading head-fi. Right out of the headphone output of the 737 sounds fantastic. Can it get better? Only one way to find out.
I haven't come across a headphone out that has been able to duplicate the sonic quality of the HE-500 via speaker taps. The best I have heard it is via the speaker taps of a 25WPC solid state amp (5.3 watts @ 38 ohms). We are into flower-bed territory so any descriptions of the sound would fail. The only thing to do is to at least try it out to see what the sonic differences may be and whether it's worth the effort.