I'm not so sure it's a matter of right or wrong. I would say it depends on the circumstance.
From my perspective, I would always choose balanced connections, analogue or digital, when presented the opportunity. (vs USB, coax, or optical)
In the case of the Pi-digital player, there is no balanced connection option. Using a Coax digital connection would be the next obvious choice (vs. optical and HDMI). The USB option would also be a good choice depending on the DAC, as articulated in the Bryston Pi-digial player manual, here:
Prior to powering on your BDP-π, connect your BDP-π to your DAC using one of the four different methods described above. The most desirable connection depends on your DAC. Typically, S/PDIF will be better sounding than TOSLINK. USB offers very high sound quality (perhaps even superior to S/ PDIF) when coupled with asynchronous USB DACs such as Bryston's own BDA-2 and BDA-3. HDMI is limited to a maximum sample rate of 48kHz and bit depth of 16."
So, L Dickman, I would say it depends. But go with balanced connection every time, if you can.