I tried it and I don't know if it is placebo or not but I now I feel more difference between the mid and the highs, like with 2 different planes, wtf? Is Klipsch informed of that? I bought the Fives for their eARC connection...
EDIT: After playing BF2042, listen music and watch some movie scenes, I can confirm there are sound differences between HDMI Arc and toshlink, wirh toshlink the sound is more "open", has more 3D effects and has more "air" because the mids and highs are highly improved. With HDMI Arc the sound is more plane, less 3D effects, feels a very muffed and without personality.