Both the sounds from the 808 kit and the 909 kit are available to be played simultaneously. The quoted polyphony for the D-Station is for 8 simultaneous drum sounds. This is the maximum polyphony. However, the amount of processing power required to produce some voices can vary a great deal. For example, a 909 tom uses nearly 28% of the total processing power of the D-Station, but to create an 808 closed hi-hat uses under 10%. So in reality, the polyphony is dependent on the types of voices used. Typically, there will not be a use for 3 toms at once, so the available processing power should be adequate for most situations.