Xfinity cable box directly to amp produces notably superior SQ than cable box > DAC > amp

In the process of A/B ing a Benchmark Dac1 vs a MusicHall Dac 25.3 with the objective of choosing a favorite SQ, I discovered that when going from my xfinity cable tv box directly to my amp by way of RCA stereo interconnects, the SQ was clearly superior (wider/deeper soundstage, more defined/prominent lower end, cleaner all around) to connecting that same cable tv box to both the Benchmark and the MusicHall DACs (via toslink) and then to my amp (via RCA interconnects).

I'm hoping someone can help explain this to me because I'm baffled by this. I've always assumed that converting a digital signal to analog by way of a superior device such as these two dacs, would provide a value ADD to using the dac inside the cable tv box to produce the analog sound. What am I missing here?

Using identical interconnects and toggling from Line 1 to Line 2 inputs on my amp, where line 1 is Xfinity>amp and line 2 is xfinity > dac> amp. I've ruled out the possibility that there could be something going on w my Line level inputs on my amp by flipping the line1 and line 2 during the test.  I’ve also confirmed that the xfinity audio device settings are set to stereo audio (PCM) output for optical. Here are the only explanations I can think of:

1) Both the Benchmark and MusicHall Dac are damaged.

2) The toslink cable I'm using is damaged.

3) There is something configuration related with respect to the audio signal being put out by the xfinity box.

Can someone help shine some light on this?