The inserts on the mixer are on TRS (tip/ring/sleeve) connectors. They are two-way output/input connections that are "normalled" so when nothing's connected they just pass the signal on to the next stage of the channel. The trick is to tap (like a keg) a copy of that signal, sending it to the recorder while also retaining the "normal" path. So what you need is eight special cables that act as splitters. On one end they would have the RCA connectors and on the other end they would have TRS plugs, with the tip and ring wired together. That TRS end would act as the splitter, keeping the internal signal path intact but also connecting it to the recorder.
I don't know if there's an appropriate cable on the market, but it's an easy build if you can solder. It might be most cost and time effective to buy an RCA snake and replace one end with appropriately wired TRS. Tip of the RCA end connects to tip and ring of the TRS end, that simple.