Update:
In April, I came across an absolute mint condition Anthem STR Preamplifier on Audiogon that was about 100 miles away for an incredible price. These STR Preamps and power amps always sell in one or two days, so booked it over there and was able thoroughly inspect the unit and all accessories. It was as advertised in mint condition, looking like it had never been taken out of the box. It was apparent that this seller meticulously takes care of his equipment. Super guy as well.
So, I snapped it up on the spot. I figured that I was getting a preamp that was at least as good as the PS Audio Stellar Gain Cell and which also offers ARC and both MM and MC phono inputs. Also, the STR Preamp had a very positive review over at Audioholics.
Having listened to the STR for a few months now, I do believe the sound is superior. And, no, I don't believe it is a case of confirmation or expectation bias, as I am pretty skeptical of manufacturer claims by nature and, because of my readings here, I was determined to not allow any such bias affect my impression of the STR. Hence, I did not want to write any sort of immediate impression of the STR, but rather, wanted to use it for a while before passing any judgement.
My immediate and continuing impression is that the STR does have a smoother and less irritating sound to it. Amir's review of the Stellar Gain showed pretty bad distortion levels that were worse even than all of the AVRs tested. Some here at ARS said the Stellar Gain's distortion might be audible, while others questioned that. Also, the STR seems to have a bit more attack and immediacy to the sound. Perhaps the biggest difference is that the STR seems to be superior in the placement of different vocalists and instruments in the sound stage. The voices seem to exist in their particular space better than they did with the Stellar Gain. Perhaps the output stage is superior.
Thanks to all here for the suggestions and information provided!