I looked it up for you. This is the text from the general music web site that time. It is almost vintage

I wouldn't know, why they called it PII, my lucky guess they had a Powerstation, with no extra RAM or with different (or no) software on the hard disk.

WK4 Power Station II, a special version of the WK4 World Keyboard fitted with a 540 MB internal hard disk (2.5" - IDE interface), is now available at music stores everywhere. The internal hard disk is an important innovation for all musicians, allowing any piece of data used (songs, styles, performances, etc) to be rationally stored and handled with speed and accuracy. It takes less than 10 second to load 16 songs into memory, and less than 15 seconds to load an entire block of songs complete with their relative PCM samples (2 MB).

The other amazing feature of WK4 Power Station II is the vast amount of software supplied in its hard disk:

Over 700 songs, representing the very best of a wide variety of musical styles, including International hits, Italian hits, Spanish hits, Italian dancehall, Traditional songs, and others.

120 styles, with new PROFILES specifically developed for WK4 and a selection from the fully compatible WX/SX library.

50 MB of new sounds (immediately utilizable, thanks to the 2 MB DRAM with back-up battery already installed) including pads, vintage organs, acoustic pianos, choirs, strings, orchestral, accordions, basses, drum kits, techno, grooves, sound effects, ethnic instruments (Arabic percussions, Chinese sounds, Brazilian loops, etc) and of others.

WK4 Power Station II is an absolutely complete workstation, the ideal instrument for all musicians working professionally in the field of live entertainment and music-bars.
* Polyphony 64 notes max.
* 600 editable sounds
* Sample RAM expandable up to 32 MB with SIMM modules
* 4 programmable digital effects processors
* 128 styles (96 ROM + 32 programmable), each with 4 variations
* Ample disk library
* Compatible with SMF 0, 1 and 1+lyrics, and with WX/SX and GMX formats
* Sequencer: 32 tracks, 250,000 events, microscope editing, background loading
* Professional master keyboard (aftertouch, 32 layers, 32 splits, 3 programmable pedals, 2 MIDI In, 2 Out, 2 Thru)
* Operating system updatable with new functions via disk
* Optional Audio/Video interface for displaying melody, chords and lyrics on any TV, and for processing external signals by internal effects
* 2-way stereo amplification with four speakers (25W + 25W).

greetings!

Joost