Hasn't
@Wiimer iirc done that as a proof on concept using a mini grouped with another WiiM device using peq etc?
Yes, I did it.
This generally works well, but if you group two WiiMs and connect the Sub wirelessly, you need to turn off "Per-Source Volume Control." Otherwise, if you adjust the volume on the lead device after switching inputs, the volume on the follower device will no longer sync. I also think you won’t be able to use pre-gain. (This isn’t a problem if there’s only one source.)
I wasn't aware that the sub used wireless connection. I'm suggesting a transmitter that plugs into the sub out port and a receiver that plugs into the LFE input of an active sub (not a Wiim sub). Does the WAP/WAU send a full range signal to the sub via BT, or is it the sub out signal?
As things stand, using a Bluetooth adapter might be the most practical solution.
However, since the Ultra supports DLNA Cast, you can output wirelessly by connecting the Mini to the subwoofer. If simultaneous output via DLNA Cast and Line-out becomes possible, this could potentially be used as a Sub-out.
If WiiM is to release an ultra-compact DLNA Cast transceiver adapter, it would allow wired headphones to go wireless, which I personally interesting.
Btw, based on my testing, the audio latency for DLNA Cast is at least around 100 ms, so it seems like the Ultra’s Subwoofer-Sync could handle it.
(No, there are even more delays..)
Another advantage is that the volume issue mentioned earlier does not occur in this case.