Why can't I browse the internet when streaming music?

I am using a Mid 2012 MBP in tip top shape and I have 24MB/s ADSL 2+ with current speed test results of 12.34 Mbps line speed and 1.51 MB/s dl speed. I have 3 things connected to my router MBP, iPhone and Apple TV. Router is D-Link N750. All items listed have latest firmware, updates etc.

My problem is that whenever I am streaming music, either with Spotify or iTunes Radio etc my browsing speed becomes almost unusable and when I then play the music through the Apple TV with Airplay the streaming drops out all the time and I cannot use the internet at all. I have turned off high bitrate streaming etc but nothing is helping.

When I stream through the iPhone on the wireless it all seems to work fine so I think the problem is with the MBP. I have tried reseting PRAM, deleting com.apple.internetconfig.plst etc. but no difference.

Pls help, this is driving me insane!