It is difficult to say how they will sound together, I guess you can only take a risk and try. By default, WISA devices from different vendors should work together and I believe they do - same principle as for example 802.11ac wireless.

I would still recommend to consider second-hand Transmitter plus either an Essence Mk2 or Core. Cheapest combo of the above you will be able to buy used from eBay could be roughly 600-700 EUR and I assume that shouldn‘t be very far from a new device from HK or Klipsch.

Especially if you own BL17 already, or you specifically like their sound. You can config B&O devices so that they „know“ that BL 17s are connected, and the playback/DSP is actually adjusted to achieve best possible and most accurate sound. This obviously you can‘t achieve with other vendors as they don‘t know sonic behaviour of BL17s. I believe more experienced users like MM can probably add few more details to this. Btw, I have a pair of BL 17 WISA-connected to Moment and I love them.