I2S Input - Is It Better?

I think think you need a special cable, even though it looks like an HDMI cable.  As to whether or not it’s better, let your ears be the judge

It's a regular HDMI.  Some use an RJ45 connection. 

Generally the i2s output will yield a more accurate, cleaner sound. Tighter imaging and placement within the soundstage. Bass tends to get more defined.

This can come at the expense of sounding lean. 

Unfortunately there aren't many audiophile type HDMI cables as they are mainly for video

It depends, it looks like an HDMI cable and some companies use the same pin out but leave some disconnected. Some use their own pin out so you need to look in you manual it should show you. If they're both the same brand they will probably work together if not you might have to open them up and set jumpers. 

Unfortunately there aren't many audiophile type HDMI cables as they are mainly for video

Why, sure there is 
The following Audiophile Cable companies make HDMI cables
Acoustic Zen
Analysis Plus
Audioquest
Chord 
Crystal
Dh Labs
Furutech
Harmonic Technologies
Kinber Kable
Purist Audio Design
Straightwire
Van Den Hul
VooDoo Cable
Wireworld Cable Technology
Black Cat Cables
Nordost
Morrow Audio

and that is not all