I have/had the Pass INT-250, XA25, XA30.8. This thread inspired me to try the Coda S5.5, which I just purchased second hand. My thoughts are that the S5.5 sounds very much like the XA30.8 in tone, but with greater resolution and speed in the bass and treble. You give up some weight, palpability and ease in the overall sound. Swapping power and signal cables I can make the two sound nearly identical; although you cannot ultimately make the Coda as dense or relaxed as the Pass or the Pass as resolute and lively as the Coda there is a region where the two amps greatly overlap. My impression is that the XA30.8 prefers balanced sources while the Coda plays better with single ended sources. The Coda runs much cooler and is easier to move around, but as others have mentioned the speaker inputs are crossed in the back with the left side on the right of the amp and vice versa. Which amp sounds better to you will likely depend on other components in your chain and personal preference.
I no longer have the XA25 or the INT-250, but my recollection is that these are much different sounding sonically, with the XA25 lacking the dynamic capability of these others while sounding faster and leaner and less relaxed, particularly in the upper midrange and treble. It still shares the Pass house sound though of great refinement and large center image. The INT-250 was my least favorite. It sounded kind of grey and washed out to me lacking the harmonic richness and colors of the other amps despite sounding overall warm, robust and dynamically powerful.