Delsys devices are not designed to be used with stimulation devices.
The fundamental performance issue is the amplitude of the detected stimulus as recorded by the DE-2.1 sensor. An amplitude at the recording site that exceeds +/-5mV will saturate the system. This may cause the artifact tail to extend for some time before the amplifiers recover. If the latency of your evoked response is short, the information of interest may be masked in the artifact tail.
The sensors are powered with +/-5V. An input signal below this value may cause saturation but should not cause damage. Inputs above +/-5V should be presented with caution, as voltages exceeding this range may damage sensitive components.
The true amplitude of the detected artifact is generally unknown apriori, since the stimulus undergoes a transformation as it traverses the body as a volume-conducted wave. This artifact is often quite large and may mask the evoked signal of interest. Latency between artifact and evoked response is generally maximized so that the effect of the artifact tail on the signal is diminished.