Just installed a bluesound node 2i , quality not so good

if u are using node 2i analog outputs - well then yes, the sound is mediocre at best

most who are serious about good sound quality from streamed sources through the node 2i will use its digital output and run it into an separate dac

"And wired to analogue inputs of avr"

There's a big part of your problem right there.  Sound quality out of the analog outputs is pretty decent given the price point, but using a better DAC will improve sound quality.

I just received my new 2i yesterday. I already have a 2. So,as a little test, set up 2i via analog outputs. I listened to a couple of songs. I thought it sounded really good. Then I ran it through my DAC, played the same songs. I noticed better detail. The biggest thing I noticed was much,much larger soundstage,as well as better defined 3D soundstage. 

2i sounds great on my system.

IMHO the Bluesound products weakest link has always been its onboard DAC.
The single ended analog outputs leave a lot to be desired for a serious music system.
Even a $250 DAC will yield benefits but has to have toslink or coax input as no USB digital output on the 2i.

Good luck and stay safe