the optical rendu is legit (excellent at doing what they say it does)... as is the swenson uptone ether-regen (and the network acoustics passive stuff)... allows users to achieve a superb level of cleanliness and clarity in the digital feed into a streamer or dac for a (fairly) modest cost ... etherregen has an added benefit of allowing an outboard 10mhz clock to further solidify the signal
some upper tier integrated streamer/dac makers build in some of these capabilities into their units these days, making the abovementioned pieces potentially duplicative... but i have felt on the integrated units it is somewhat hard to tell what is doing what as you can only hear the end result processed through the combination of built in ’stages’