ARC is a crap shoot at best. The reason why so many dealers stay far away from that BS. There are a few that have discovered specific equipment models, that actual work together and offer that package to customers. They are brave souls, since a firmware update could come any day and break it.
I would say your best bet (to save yourself time & aggravation) is to get the 50' optical cable and run it.

Now about that 50' HDMI cable. What brand are you using? I'm guessing you are only sending 1080p to your TV at this point. Noway you can make me believe you are sending 4K over that distance on a passive cable.