No idea, I’ve not done any investigation on the Brennan, as I don’t own one, but there aren’t that many radio stations that don’t play on Sonos, with the multiple streamers they support, from TuneIn, iHeart roadie, radio.com, and others.
Because Sonos is designed as a whole home system, to play a stream in all “rooms” in sync, any input has a certain delay associated with it, so that Sonos can be sure it will play in sync. This is not a problem at all when you’re only using Sonos speakers, in fact it’s a benefit, and completely transparent to the user. It’s only when you’re trying to add non Sonos systems, usually a Port connected to an amplifier. In that case, if the source is from the Sonos to the amplifier, all speakers are in sync. It’s when the source is the amplifier that the Sonos speakers will be delayed from the amplifier’s speakers.