I'm confused by the DAC behind a DAC comment as the KTB does not have an output that could feed another DAC unless you use a VIM SBC also, which seems not to be the case for you as you are using a Pi. If you are using the KTB with a VIM then apparently you can output S/PDIF that could then be used to feed another DAC, which seems a bit of a waste as you could simply use a cheaper option, such as a Digi+ HAT for the Pi.
I use a Pi 3 with a KTB and have used them in the following configurations:
- PI -> USB -> KTB -> Amplifier
- Pi + Digi+ -> Coax S/PDIF -> KTB -> Amplifier
The Pi 3 (and possibly the Pi 2) shares the same controller for the USB and ethernet port and some indicate that there could be noise/jitter/interference introduced if using the USB to feed the KTB. I use wired ethernet for my PIs, but can't recall any bad effects. Others may have other experiences and measurements around this, but maybe try using the Pi 2 -> USB -> KTB -> amplifier chain first, before buying the Digi+. It may be good enough.