Hey sim_audio_nerd,
I'm very familiar with your XA30.8 amplifier. Actually your amp and the XA-25 are my favorite amplifiers in the .8 generation of Pass Labs amplifiers.
I don't believe that the Coda S5.5 would be a lateral move for the following reasons. The S5.5 compared to your XA30.8 will have a more airy/open detailed top end, will present more easily heard micro-details because its noise floor is lower, will be overall more dynamic/faster, and have a more controlled/tighter bottom end. If these differences appeal to your sonic palette you would totally enjoy the S5.5. The XA30.8 is a great amplifier, and so is the S5.5, so which is better is based on your personal taste and how each amplifier matches up with the speakers in your system.
Teajay