Kops, you can go to AES/EBU, S/PDIF or TOSLINK to achieve 192 kHz/24-bit operation with the Playback Designs today.
I'm not sure what you mean when you say "future proof". With USB, the PD's firmware can be updated (it has been a couple of times since I've owned mine) and there are ample ways to use external devices to obtain 192/24 operation in the current hardware/firmware configuration. No device is likely to cover all potential future hardware possibilities, since we won't know them until we see them.
Dave
I'm not sure what you mean when you say "future proof". With USB, the PD's firmware can be updated (it has been a couple of times since I've owned mine) and there are ample ways to use external devices to obtain 192/24 operation in the current hardware/firmware configuration. No device is likely to cover all potential future hardware possibilities, since we won't know them until we see them.
Dave