Besides the material at the antenna connector, maybe an observation to add …
I have never had any problem with the standard antenna (the strip with the glue layer). Only …
If the antenna is surrounded by metal, it will not work. I have experienced many times that if the WiFi signal received by the Up2Stream is not strong enough, the speaker can produce crackling noise.
My advise would be to work with a rod antenna and place it on the back plate of your AKAI receiver. @SimonB has done this several times. Here you can find one of his posts with an example of implementing a Mini with a rod antenna in a Hitachi receiver.
Pay attention to the picture below (or the 5th picture in his post) that shows the rod antenna mount.
In his 2nd picture you see the inside of the Hitachi receiver, the position of the Mini, and the WiFi antenna cable going to the rod antenna on the back plate.
Good luck solving this!