GazzaBloom's post in No sound from Helix SPDIF via Focusrite Saffire Pro 14 was marked as the answer
OK So I have established that it's not a fault with the Helix. I tested the Helix into another audio receiver with a digital coax input and It received digital audio from the Helix OK.
The issue is at the Saffire interface end
GazzaBloom's post in Don't update the the new yosemite released April 8 , 2015 (today) yet or POD HD will not be recognized was marked as the answer
Works fine here with POD HD500X, Mid 2010 iMac, no re-install of driver required.
GazzaBloom's post in How to make the Greenback 25s less dark was marked as the answer
While I don't use the Greenback cab much myself I suggest you try tweaking the cab lo cut parameter, I find that this can remove a lot of the apparent harsh low end in some of the cabs. I play along to a recording that I like and tweak the tone to make my guitar sit correctly in the mix. I've found that a lot of low end and high needs cutting and the mid range often needs boosting. It can sound a little mid heavy on it's own but in a full band mix will sound just right.