But am I right from other posts that it would work via the USB-C on my MacBook straight to the phones? I have quite a bit of lossless music on my laptop and this would be interesting to try. Would there be any difference from using the 3.5mm jack on my Mac?
I only listen to 1411 kbps lossless (Tidal Hifi streaming or downloads). This works fine via Bluetooth and USB-C and sounds clearly better than the lossy streams from Apple Music or Spotify.
While you'd expect USB-C to sound much better without the Bluetooth 'bottleneck' from the SBC, AAC or AptX codecs, I've found this is not to be the case. B&W confirmed this too btw. With the PX, the signal or datastream
always goes through its own DAC and signal processing including upsampling to 768kHz. etc. Regardless the type of connection used. I didn't try the analog 3.5 jack yet for music but this one is likely to provide the lowest sound quality. Especially if you're not using a separate high-end / audiophile DAC. In any case, using a 3.5mm jack you'll be adding an extra (unneeded) DA conversion + amplification at the source side (your laptop / phone / separate DAC) that still feeds the PX's own DAC that - again - will do another A-D and D-A conversion, processing + amplification. This repoduction chain is not likely to give the best results. With passive wired headphones the situation is totally different. I think most - if not all - ANC headphones are like the PX in this respect but I'm not sure.
From my laptop (HP - Windows10), USB-C plays a lot louder than Bluetooth (AptX). But if you set the volume level the same, there is very little difference in sound quality between BT and USB-C. On
some good recordings there is a little more bass extension and the treble seems a tiny bit cleaner. But as you only hear this on very good recordings, even then the difference is never more than
very small. Not worth getting wired-up for imo. But the connections are there so why not try and compare them yourself?
B&W is very clear about the best possible sound quality from the PX. AptX HD. I hope more laptops will support AptX HD soon. Or maybe even the iPhone/iPad at some point but I doubt that.