Rpi2/3 with Allo Boss and Volt+ Stepped - Wifi unstable

Hello,

My 1st post on this excellent product.

I might have stumbled upon a unstable situation, for which I call your help.

Setup :
RPI2 with a Realtel USB wifi or RPI3 with onboard or USB realtek USB (both have the issue)
With a Boss Hat (v1.2)
Connected to a Volt+ with Stepped attenuator (great sound btw)
Image 2.348 (after upgrading from 2.323)
Speak set old skool Wigo WB25

Issue :
When playing a webradio, everything works ok, and very smoothly. But when trying to go thru Airplay, network drops/becomes extermely slow (20000+ ms) until I shut the airplay on my phone or mac, and wait a few minutes, and then it comes back to normal. Music starts but is absolutely no what you would expected - gigantic lag of course with this kind on network connection.
This doesn’t happen when using a hardwire.

Known issue? What do I do wrong? Does the speaker set or/and the attenuator kill my wifi connection?
Honestly I’m out of clues.

Regards
Tim