Would offer a friendly challenge for an objective, or even subjective proof of the E6 improving the sound of the Clip+. I don't think it would do any good, and might actually do some harm.
Copy pasted measurements of the Clip+:
- Frequency Response: Ruler flat from 10 hz to 20 Khz and very accurate
- Distortion: Below 0.05% which most agree is inaudible
- Maximum Output: About 15 mW--higher than average
- Output Impedance: An extremely impressive 1 ohm (dedicated headphone amp territory)
Plenty of clean power to drive all efficient headphones you're likely to pair with the DAP. Would also challenge your claim on the players being woolly, lacking in soundstage and unclear (same as woolly?). It's razor clean to my ears and neutral as all get out. Nothing is modified or added, which might account for the euphonic sound from hisoundaudio players (not a knock on their DAP).
Have briefly auditioned hisoundaudio and personally couldn't deal with the hiss, spoiled by the noiseless backgrounds I'm used to from on-ear headphone listening with DAC/AMP pairings. To each their own of course! If you like the E6+Clip pairing, then by all means continue to do so.