Hey RG, it seems (though not shown on the diagrams on pg 17) that there is a direct L/R bus that the Fx chain mixes back into (Dirct: Direct level), so on a mixer this would be like the the preamp output routed/assigned direct to the main L/R outs. The Fx chain is then mixed into this bus controlled overall by the last effector in the chains output level. Apart from Eq (which is strictly serial (in the Fx chain) when it's in), all the other Fxs let you mix (they call it balance) the amount of effect with whatever their input signal is (i.e. from the previous effector/unit in the chain). So these all mix into the Fx chain in parallel and the whole Fx chain is like a parallel loop (send/retrn) with the dry signal. So having the last effector/unit in the chain (normally reverb) at 100% wet is how you'd do it with a mixer as it is then being mixed with the dry input signal (controlled by the Dirct: Direct Level) and the last effector units output level. So think 4 faders, panned L/R in pairs, 1&2 are direct (MP1), and 3&4 is the Fx return all assigned to the main mix bus.
The effector chain is like (conceptually) a separate mixer with a stereo send for each effector all coming back into separate L/R channel pairs which have their own sends (like on a mixer). This isn't quite as versatile as a mixer in that the effectors are in a preset (algorithm) order (albeit variable to some extent).