Same here, but I did get the Silentwing 3 (x2) as intake and it is not quieter by any stretch. IMO it just have the posibility of getting even louder than the purewing. Don't get me wrong tho! There are silent until approx. 55%-60% but pass that !! They are as loud as the purewing or maybe even worst.
With that said :
'' I went on Noctua's site and I don't understand if their redux serie is only package redux or also quality redux ?''
Their Redux line-up use their SSO bearings instead of the SSO2 (upgraded version). The package will comme with the fan and screws. No spliters, no vibration pads and the most obvious : grey on grey. (I have nf-p12 and nf-p12 redux and imo, their the same but a bit louder at high rpm)
'' Is there any point to put noctua's LNA adapters between fans and a PWM fan hub ? ''
Yes as it will reduce the max speed, therefore the sound.
I don't have answer to the 2nd one but I'd guess you'd be ok since I do it and my pc didn't explode. BUT i don't have an real explanation for you on that one.
And for what I would do ? as much as a noctua lover that I am, there aren't cheap. So I went on the P14 (by arctic) route to see if it's any brighter there.
Hope it help.