There are no new M-ATX motherboards for the 970/990FX platform right now. Only the old 760G chipset ones, which I would avoid using with the FX-8320. Those motherboards are not ideal for the power delivery the 8320 requires.
If you still would go for the M-ATX route, I'd suggest the GIGABYTE GA-78LMT-USB3 (would still require update).
You should go full ATX if you want a good motherboard for that CPU.