Hello Tim,

> Thanks so much for your helpful (and sobering) replies!  If I had spent
> $50 (instead of $260) for this card, I would have already trashed it and
> just bought the Nvidia one (Quadro K1200)!  Clearly AMD is not a panacea
> for Linux video cards!  I may still do that, or maybe try to return it.)
>

AMDGPU drivers usually works great on Linux, as they are the same
drivers shipped by Amd minus the proprietary stuff. radeon is the old
opensource project, nobody really should use it anymore unless amdgpu
isn't working for them. A work around for your problem could be to
remove the other drivers (xserver-xorg-video-ati and
xserver-xorg-video-radeon), leaving only amdgpu to be loaded. Make sure
firmware-amd-graphics is installed, backports if possible.

Don't forget to install the backports of mesa, to get the latest
available drivers. ASCII uses pretty old software, and in your case you
really want something more recent if not the most recent.

When it comes to drivers and the kernel, there is almost no reason for
anybody to not use backports.

> Ludovic, I don't have the card installed right now, but the family is
> VERDE as seen in this old Xorg output: (--) RADEON(0): Chipset: "VERDE"
> (ChipID = 0x682c)
>

CAPE VERDE is of the Southern Islands family.
The amdgpu driver supports SI and newer families' video cards.

You should be good.

Ludovic