I think inserts and sends are always processed in numerical order, i.e. FX 1, FX 2 etc. This equates to all the effects being in serial.

You could, however, use group tracks to make a parallel FX arrangement. Start with multiple copies of a track, and apply one effect to each copy of the track. Route all these copies of the track through the same group. Voila, the group track has the FX applied in parallel