well, why not?
I edited my sources.list to this:
deb http://deb.debian.org/debian/ unstable main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian/ unstable main contrib non-free non-free-firmware
deb http://security.debian.org/debian-security/ trixie-security/updates main contrib non-free non-free-firmware
deb-src http://security.debian.org/debian-security/ trixie-security/updates main contrib non-free non-free-firmware
deb http://deb.debian.org/debian trixie-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian trixie-updates main contrib non-free non-free-firmware
deb http://deb-multimedia.org/ unstable main non-free
seems to be fine.
perhaps the APTus Upgrade Checker will fail, dunno