looking for such a machine (CS6r is the rack version)."
The best options are the Motif ES/S90ES keyboards and the Motif ES rack. The keyboards can host three PLG150 boards, the rack can host two of them. All of these instruments have great acoustic/electric pianos and a full complement of romper sounds. In addition to the AN1X-related PLG-150AN there were also DX-7 and VL-70 PLG-150 boards. The later Motifs such as the XS and XF models can't host PLG boards.
There isn't much control of the PLG-150AN parameters from the front panels of these instruments. There is a good editor/librarian, but I'm not sure if it works on anything beyond Windows XP. The PLG-150AN is a bit different from the AN1X. Each card has five-voice polyphony, and morphing is limited to one target program. The PLG-150AN has a SuperSaw waveform added, and I've heard it was tweaked to sound as close to the Prophet V as possible.
Jim Harp