The Beolab 17 would always use its own DAC for TOSLINK and wireless. There's not really enough info in that post about the 17s to determine level matching, toslink parameters, source material, etc.
The 17s are a digital speaker. Here's a block diagram of it. All the analog inputs go through an ADC and then the same DSP as the digital in and then the same DAC as the digital in. Nothing is connected directly to the amp. So I don't know what the poster in that other thread is measuring, but it's not the performance of the Beolab's DAC. This figure is from the 17's service manual.
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The 17s do have an acoustic lens for the tweeter, so they are pretty focused on a main listening position. If you stand in different places, they will sound different. I'm not sure if the poster on the 17 listened to them in the same spot.
B&O gear is, IMO, primarily for the looks and style and secondarily for the sound. I had B&O for maybe 20 years. It's good sound, but it's excellent style. I had Penta 5 and Beloab 4500 and Beolab 6000, none of the newer stuff.
I'd say go to a B&O store and listen to them over wireless on songs you know well. Of course, that will likely be in a treated room, so YMMV at home.
B&O put a lot of effort into their wireless system (and thus DAC), so my presumption would be that it's not crap. But of course, I'd want to hear/measure them in a controlled experiment. I would want to see more quantitative results than one person's anecdote.
Maybe this is of some help
#77 in a series of articles about the technology behind Bang & Olufsen loudspeakers I’m occasionally asked about the technical details of connecting Bang & Olufsen…
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