The story is simple:
The GVP-SCSI (just like the A2091) is a Z2-DMA-card, and can therefore
only do DMA to the 1st 16mb address-space. The only RAM you will find
in there on an A3000/4000 is the chip-mem (or RAM on Z2-cards).
Everything outside will cause an error and a switchback to PIO.
