@MiAmigo:
If you get the scandoubler for the CV64/3D, you will get the Amigas native chipset output doubled to 31.5 kHz (displayable with a normal VGA-monitor) through the same monitor-port as the CV64/3D card itself outputs graphics and it switches automatically between those two sources.
You are indeed right - you can't use Zorro3-only cards like the DKB3128 or the Phase5 Fastlane in the A2000. You could add 4MB extra 16-bit FastMem on a Zorro2 card, but it will be very slow. The maximum amount of memory you can add to a card on the Zorro2-bus is actually 8MB, but as your CV64/3D already uses 4MB of the 8MB Zorro2 address-space you cant add that much.
/Patrik