Probably some good scientific reason for not crossing current paths.
I think that the 'crossing of currents', from single channel units that Rojo refers to, means that a proportion or all the RF currents from each active would be returned via the the other unit's neutral plate since the neutrals would be common RF returns both connnected to the patient. I suppose the RF active currents would have to be compatible i.e. two similar single channel units being used.
Return currents in each circuit would have to be within acceptible tolerances (similar to active currents) but 'crossed current paths' might cause unexpected or less predictable return paths that might pass through tissues sensitive to heating that need to be avoided. Especially if the neutral plates are widely spaced apart and positioned at different sites.
