S4X 1.3 version is acoustically identical to the 1.2 version but with the USC calibration plugin included. This improves their flat frequency response from ~2dB down to ~1dB tolerance using DSP.
S4X 1.0 has female jacks mounted on the panel with a straight down cable position. S4X 1.1 has an angled cable position that enables front and back cable position depending on the use case. They are “flippable”. S4X 1.2 is the same as 1.1 but with embedded connectors for greater durability.
Regarding S4X vs S5X tuning, the S4X are slightly darker sounding and warm. They represent how a common room will sound. That, together with acoustics properties, makes them a staple in over 10,000 studios worldwide for mixing and producing in stereo. The S5X are specifically tuned for spatial audio mixing with a brighter character that helps with 360 positioning and movements of 3D binauralised audio (e.g., Dolby Atmos). Both are tuned flat for their purpose. It’s not one target frequency response curve that fits all use cases.
Regarding S4X vs S4R tuning, the S4X is more laid back in comparison to S4R tuning that is made with clarity in mind. That is to deliver accurate monitoring for recording and podcasting sessions. Mids forward tuning is welcomed in monitoring for details and dynamics. Both of these are crucial when you’re recording instruments or vocals at the highest level.