I think hifichris will be your best bet. I'm sure he Mentioned the DX90 in his review of the Plenue D on his German site. I think jmills8 has one also.
Thanks, I will PM Chris.
I heard my name drop, so here I am.
It wasn't really a review on my German site, just some impressions in note form.
Anyway, the sound quality from my very subjective point of view (only had the Plenue D for two days before I sold it btw., all impressions without BBE/EQ, I am not sure at the moment whether I volume-matched both DAPs when the Cowon was still in the house): both have got got excellent clarity and transparancy, but while I found the Plenue D to sound spot-on neutral (in my ears, it doesn't sound any dark, analogue or smooth as others have reported, just perfectly spot-on uncoloured and neutral), the DX90 appeared "faster" in the treble, hence a bit brighter sounding (the cliché'd Sabre glare which I personally love, if one can say so). None sounds really coloured to me th and properly volume-matched, the differences are rather small nuances than night and day, but can be important for finding one's last 5% of sound preference.
Identical bass speed, DX90's soundstage wider and better separated, Plenue D's more compact ("average"). Clearly not as large/immersive and well-separated and layered as DX90's or DX80's stage (the latter has just as much width as the DX90 in my ears, while adding more spatial depth to create a really deep and expansive field of sound, however I find the DX80 to be more on the organic and warm side).
Both (getting back to the Plenue D and DX90) have very little hiss levels, DX90 even less to the extent of being just barely audible in a quiet room with super sensitive IEMs when a track with computer-generated silence is playing (I don't know of any DAP with less than 1 Ohm output impedance that has less hiss than the DX90 - if you know one, let me know).
Not sure about volume step size, but both feature a fine-grained volume control, however the Plenue D's lowest possible volume setting is so much louder than the DX90 at around 110 with very sensitive IEMs like the SE846 (the DX90 will give you the much better ability to listen at super low volume whereas the Plenue D already puts out rather high voltage at 1/100, which was the main reason why I sold it - if they fix it one day or if it gains RockBox support, I'll probably buy it again, as the pretty neutral, transparent sound with good hiss performance and low output impedance were keepers).
