It seems to me that you are doing lots of things that make the two sources more blurred and more alike than different. If you want to hear the two sources, then take out all the other crap and compare Mac > Reimyo > G-Lite and then Mac > Parasound > G-Lite. Use the same cables to the extent you can, definitely using the same Toslink and the same RCAs, and just do a straight-up comparison listening to one and then the other. If you really have to be able to switch back and forth, then use the Toslink splitter and plug the output of both DACs into the NAD and use the tape out. I think that will affect the comparison, but you can get the satisfaction of A > B switching.
I also may be hated for saying this, but the G-Lite is not the most resolving amplifier of all time to do comparisons on this level. If you can compare with a better amp with two inputs, then you can also remove some steps and some limitations.