I listen to the D90 a lot over my speakers (Dali Opticon 6) with a NAD Amp1 (only available in Europe) amplifier. At the moment I am also trying out NCore 400 mono blocks.
I use the D90 also a lot with a SMSL SP200 headphone amp. My headphones are Philips Fidelio L2, Philips SHP9500, Philips X2 and Sennheiser HD650.
Of course my impressions are very subjective/biased because I did not do any 'scientific' listening tests (blind listening, exact volume leveling etc.). Overall in my ears the D90 compared to the Project sounds better over all my gear.
Beware subjective audiophile terms ahead :
More openness between the instruments more depth in the soundstage, faster transients and more 'Umph'. With Umph I mean more dynamics between soft and loud passages. Subjectively for me the D90 is the best DAC I ever had until now. As I said in a previous post: A friend (who has very expensive gear) and I heard the D90 at his house and compared it to some very expensive DACS (DCS Bartok $12000 and Metrum Acoustics $6000). We where astonished about the little to none differences we heard. In our ears the D90 even sounded better than the Metrum Acoustics. Mind you, we had a nice evening with a glass of wine and where completely feeding each others bias
. But isn't that what music enjoyment is also about in the end?