RAKK DAC id / use question

hi everyone.  i bought a tuner off a guy and he threw in this DAC because he didn't feel it had any value (he didn't know what it was either).

it's a RAKK dac 24bit / 192KHz D/A Converter made by K&K Audio and i don't know what that means.  

i've called K&K Audio and left a message but it seems that his online persona (he ran the K&K forum on Audio Asylum) hasn't been around since March of this year.  i opened it up and peeked around inside and it seems to be very well planned and put together.  

i've uploaded pictures of it on my system page
https://systems.audiogon.com/systems/9572

i've had digital outputs on DATs in the past but they were optical.  i don't think i've ever seen an RCA out.  what sort of device feeds this with a single RCA input?

what does the 'lift/gnd' switch do?

and finally, what does the XO-DAC switch on the front do?  (out / in)

thanks very much.  i'm piecing together as much knowledge as i can on the analog side of this hobby and have completely ignored the digital aspect of it.