Actually, there is no question that this is the name of this instrument, because it was given by the trombone player, Russell Yoon, whose idea it was.  In case it's not obvious, the name indicates a diminutive cimbasso, the popular name for contrabass valve trombones, most often with vertical valve sections.  There's not much new in this instrument, trombones with a vertical valve section in the tenor/baritone range have been made by many makers for 150 years and I would guess that a few were made with large bores.  Larry Minick made bass valve sections, intended for use with bass trombone bell sections with two valves, for Tommy Johnson, Jim Self and others.  Those, like this one, utilize valve sections from three valve American style baritone horns.  In this case it was a three valve compensating Besson with a bore of approximately .580".  The loop of tubing that leads from the valve section to the bell receiver is .595" (the same as through the rotary valves in the bell section.  The desire was to make this as large a valve trombone as possible.  It works surprisingly well, especially in the low register.  The angle of the valves, like on front action euphoniums, is quite comfortable in playing position.  Larry Minick had also made several cimbassi with valve sections from front action tubas for the same reason and adding the fifth valve in the bell section.  So while unusual, you can see that the form of this trombone is not unique.