Not saying that digital gear cant, but that a simple format converter really really shouldn't. This is quite different than ASRC. This is (unless I am sorely mistaken) nothing more than receive and transmit, no intended alteration of the data. Heck, if you are getting significant THD+IMD, then you certainly arnt passing bit perfect.
Even something as simple as just passing HDCD and/or DSD data would be sufficient.
Ah, I figured this would be a standard measurement for something employing high speed digital design techniques and making a statement like the first one here, which is, of course, correct, since while the data stored may be digital, what is transmitted over that coaxial cable certainly doesnt consist of perfect square wave pulses.