When setting up a computer audio source this summer, I purchased the Octave II but before even listening to it I decided to switch and purchase the Hex instead.
Therefore, I cannot speak to the differences but the Hex has been quite satisfactory in my system and equal to (but a bit different than) a highly regarded disc player I still own.
The 6moons article includes reviews by three different reviewers and there are a few other reviews of the Hex out there if you search. A couple of the reviews make mention of the reviewer's observations relative to the Octave.
Here is one comment by John Darko, from his portion of the 6moons review;
The Octave could err toward leanness but the Hex fills you out with flesh and colour. Think sparkling mineral water flow for Octave but champagne cascade for the Hex. The latter spills with a broader spread of flavours and greater body.