The GS610/GS820 Multi Channel Source Measure Unit output is insulated from the cover case. Therefore, if you want to amplify the output voltage more than 1 unit (or 1 ch) you must connect the system in series. If you want to increase the output current by more than 1 unit (or 1 ch) you must connect the system in parallel. (Provided that it is within a range of maximum voltage/current or those limiter)
However, in case of a parallel connection in voltage output or series connection in current, a protection circuit may prevent normal operation and accuracy. Yokogawa cannot guarantee the operation or accuracy when there is a parallel connection in the voltage terminals or a series connection in the current terminals.
The attached file provides a detailed explanation for each case.