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?  

I would check the configuration of the cable box. It is possible that you are outputting the wrong digital format for a 2-channel DAC. The digital output format needs to be set to PCM, not AC-3.
Yep, that was my first thing I checked but sure enough the box configuration was set to 2-channel stereo which was also specified as being PCM.  I'm thinking the box may by buggy.  What does 5-channel or dolby in general sound like going through a pcm dac that cannot process dolby?  Can anyone describe that sound characteristic?  
Make sure any dynamic compression is turned off on the cable box (Side Note: I have FiOS, and I turned it off on my box, but irritated to find out, and confirmed with tech support, that On Demand/rentals still have non-defeatable dynamic compression, so I gotta use my Apple TV for rentals).
Toslink connections are always dubious and rarely the best means of connection.

Before evaluating the SQ differences of the two connection schemes, did you match the two for equal level? If not, any conclusion is also dubious.
Good point.  I tried my best to match the volume but did so by ear so not empirically.  I suppose that could effect the result. I’ve read about toslink cables being kinked or damaged. Is this common? Will look into dynamic compression. Have never heard of it. Thx 
Run a Toslink from the TV to DAC then into preamp.

That is the normal setup for TV audio.

The cable box is for video.

And get a streaming box.....Apple tv, Roku, or Amazon.

Ditch cable completely.
Sell the two dacs sit back and enjoy the sound. Strange I agree but if it works then go with it. 
Don, thx for info. I go from xfiity box to the tv by way of hdmi. So with that said you’re saying it’s preferable to go from TV to dac to amp? Doesn’t that just add an additional hop into the chain? 

Im starting to finally come around to xfinity as they recently integrated Netflix and prime video so now we get the best of everything from a single box without having to switch inputs.  I don’t think connected tv is quite there yet in terms of the UX. Xfinity box still best experience imo. 
Sometimes soundstage comes from sacrificing treble. That may very well be what you are hearing.