Technically yes, when adding a ROM block to a PC2 that has the PCX-1 TWO ROMs are required...one for the motherboard and one on the PCX-1 board itself.  The way the Pc2 manages 128 note polyphony is in this sort of left brain, right brain interleaved split, hence each 64 note engine requires its own ROM card.

The PCX-1 board should already have its own Orch ROM (PCR-1) pre-installed when it ships from Kurzweil.