I have not heard the S5.5, but have owned the #8, #16, and 07x preamp. I have also discussed the S5.5 with Doug at CODA about the appropriateness of using the S5.5 with either my Yamaha NS5000 or Magnepan LRS+ speaker. After I gave him feedback on what other amps sounded good with these speakers, he said not to get the S5.5. I am going to go with Doug's opinion on the CODA gear. He suggested the new SYSTEM 150 amp coming out next month for my needs (keeping the #16). This will be their new flagship. Things went a little pear-shaped for me with regards to affordability last week so that new CODA amp is on hold until the long term.
The S5.5 sounds ideal for speakers like my friend's crossover less prototype that can be driven by even 5 watts. For my current speakers the S5.5 is a downgrade from the #16. The S5.5 seems great for the new headphones I am getting.
I was able to figure out how to drum up the money for the headphones without selling the #16. I will have to sacrifice my fav speaker cable, Audience FrontRow (buy it again later). Amongst a few other items. Unfortunately, I have expensive tastes and low income.