Part of the Centennial Series and produced in very low quantities : in 1987, LP replay was clearly on its way out and Yamaha must have thought about it since the HX was added to the lineup four months after the others.
Very few "general" manufacturers produced such lavish phono EQ stages as the market was taken by a few "cottage" adventures : SME in Japan with the tubed and multi-awarded SPA-1HL (1981), Luxman with the contemporary E-06 and E-06a (1987/1990) or Audio Research, later on, with the PH-2 in 1992.
Pioneer didn't make one for its Exclusive series and even Sony, Denon or Victor stopped making such items when CD happened, leaving that tiny market to the Uesugi Bros. or even smaller brands - a dedicated, stand-alone, phono stage was a rarity, even when LP was king of the audio hills.
The HX-10000 "offers the epitome of sophisticated audiophile performance" : as in the CDX-10000, the HX enclosure holds two separate sub-enclosures, one with the power-supply, the other with the amplifying stages.
The global chassis is carved from 9mm (front), 5mm (top & bottom) and 3mm (back) extruded aluminium pieces.
The four double-sided glass-epoxy amplifying PCBs are each supported by five 8mm brass posts ; OFC wiring (even in the thick AC cord), 1% film caps, aluminium caps, bypassing caps, gold-plated OFC bus bars and regulations throughout. The terminals are all cut from brass and gold-plated - grounding posts included.
The four shielding boxes holding the four EQ stages are like those used in the CX-10000.
The power-supply is worthy of a power-amplifier with a beefy transformer (taken from the CX-10000) and six caps totalling... 100,000µF !
The EQ stages allow hookup of two separate turntables, each using either MC or MM cartridges, so the HX-10000 is in fact a quadruple EQ stage : phono 1L, 1R, phono 2L and 2R.
All the HX circuit rely on discrete componentry so there are no ICs and no op'amps.
Alas : this is near Invisibilia.