Information required about dual partitions on LinkSys WRT3200ACM

The primary reason for me choosing the WRT3200 was its speed, and ports in particular the USB2/estata and USB3 ports, which I was going to use a NAS to stream audio. At the moment, the WRT3200ACM falls well short of being able to do this, so I'm just going to go back to plan A and buy a QNAP NAS. When the firmware for the LinkSys improves I will buy it again (becasue afterall, I still want a modern AC capabale router which my Sky Broadband router is not capable of)
And as far as reflashing the alternative partition, how do I do this? I have a copy of the original LinkSys firmware for this model. Can I just use the GUI (Connectivity->Basic->Router Firmware Update->Manual) to load the same firmware and it will overwrite OpenWrt which is now inactive on the other partition? Thanks.