I bought the new Raspberry pi 3+ and connected it to the Pisound. I tried it yesterday but the Rpi wasn’t going beyond the rainbow color screen at the beginning.
That is, for the new Rpi you need to upload the new version of the software (in my case Raspbian).
So just make sure you have the new version, otherwise it won’t work with Pisound or anything else.
Besides this, everything seems to work perfectly and smooth with Pisound! New features are great, specially new Wifi compatible with 5Ghz.