I really doubt that anyone out there could tell the difference between line out and double amping - that is, unless one, or the other, is really bad. Back in my Walkman days, I found that my Sony's line out was far worse (measured) than its HPO. The same goes for a number of players. Besides, internal amps are so good now that you're introducing hardly any noise into the signal. The only thing to worry about is setting a volume that won't overload the outboard amp.
I agree, the D was designed that at full volume to be utilized as a line out. I have tried volume at full volume with a high quality portable amp and it's great. I've also measured the headphone jack and the typical line out voltage you want is 1.0v and measured that to be around the volume set at 59. I don't see any difference between the two.
http://www.cowonglobal.com/product_wide/PLENUED/product_page_4.php Audio Characteristics SNR 123dB THD+N 0.004% (24bit, 48kHz) Stereo Crosstalk -105dB Output 1Vrms Output Impedance 0.5Ω Volume 100 levels Output says = 1Vrms. That is typically a line out voltage value that components are set at to match each other at proper line levels for either inputs or outputs.
Small question as a don't find a clear answer. Does the cowon plenue d support otg? I'm doubting between this player, the fiio x3ii and x5ii. Both have their (dis)advantages so it's a difficult choice...
Just ripped The Beatles Live at the Hollywood Bowl to 320kbit lame 3.99 mp3 only to find it's got a significant glitch between all tracks on firmware 1.14. What's happened to gapless? It used to work.
How good do you think the D is mate? DX50 level? Much better than the old j3? I might audition it tomorrow with my Ref.1 in store.