Catherine Gramze composed on 2017-03-13 18:49 (UTC-0400):
Is Plymouth installed?
According to that URI it is a refresh of Radeon HD 7870 that apparently nobody ever updated Wikipedia to include. The Radeon HD 7870 is a Pitcairn XT (Southern Islands), originally released 5 years ago.
What I wrote was "driver that supports 'both' gfxchips". I meant these drivers:
http://mirrors.us.kernel.org/debian/pool/main/x/xserver-xorg -video-modesetting/
Simplest way to use is purge all traces of Intel, proprietary and AMD/ATI drivers, install xserver-xorg-video-modesetting, then restart. Ideally it would be used automatically by both the Pitcairn and the gfx built into whatever Intel CPU is onboard your MSI Z87-43G, assuming both are actually usable.....
I've not tried to find and read the manual for your motherboard, but it's typical that installation of a gfxcard in a PCIe slot defeats the ability to use the onboard gfx. In some cases, it is supported, but requires special BIOS configuration. It may be lack of support for your several year old Pitcairn is actually blocked by a motherboard BIOS/Firmware/Setup setting that enables use of Intel onboard gfx, not by anything Jessie is doing.