According the TTL-Converter #11075-HSS firmware, -
If user keeps camera system in TTL flash mode, then normal X-Sync speed limitation works automatically (1/250), as necessary for all underwater strobes mono-flash.
When user set Manual mode in flash menu ("WL" command), the system performs normal manual flash in all range of casual shutter speeds (up to 1/250), but in high speeds range 1/320 ... 1/8000 it works as HSS pulsating flash with variable frequency and necessary timings.
Pay attention, that HSS pulsating flash works only for Retra profile (TTL-Converter switch pos.-7), but for other uw strobes (other switch positions) at high shutter speeds the flash is simply Off automatically (but high speeds 1/320 ... 1/8000 are still available for shooting with ambient light).