That Vibra is probably not doing 16bit address decode which means accesses to 220 also mean that the card sees access to 620, A20 and E20 due to mirroring which is where the EMU8000 normally resides. This mirroring is what Creative used on their cards to place the EMU8000 in a place that wouldn't require new addresses and conflit with other stuff.
Your best bet is probably to move the CT1920 to 640/A40/E40 or 660/A60/E60 where it wouldn't get in the way of the Vibra.

Yes, it seems this is the case. I've moved the Vibra to 240h/7/3/7 and the CT1920 would work on 620h, but not 640h. I thought the AWE32 Upgrade was smarter, but it seems in reality these will basically act as two independent cards with the Goldfinch just feeding its analog output to the Vibra.

If the Vibra did full 16bit address decode there wouldn't be such a problem happening, intel saved a little money by not adding one extra logic chip for that purpose... Microsoft later mandated 16bit address decode to qualify some newer multimedia PC level.

Is there a way to check it? Try to talk to the Vibra via 620h and see if it responds?

On an ISA card it is easy, you count the pins on the left side on the 8bit section. Number of pins tells you how many bits it decodes, old cards have only 10, less old cards have 12 and newest cards have 16.
For onboard there's no easy telling, and the behaviour you get suggests that only 12 bit decode is done and there isn't anything one can do about it without whipping up a soldering iron and modding the board a little.