Please help me to understand how set an insertion effect DSP 3 as system effect on YAMAHA 9000 PRO in order to apply some effect types ( ROOM SIZE ) to microphone sound.

I attached the page from manual who said that DSP 3 can be set either as system effect or insertion effect but I failed to discover how. .Thanks

Hi Laurian,
Technically speaking, the Yamaha PSR-9000Pro was not a product of the synthesizer department, although it had many features that crossed over from traditional Arranger Keyboards into the realm of the Synthesizer. Combining Sampling and Modular Synthesis Plugin System expansion boards, it was the pre-cursor to the Tyros-line (which is now the GENOS).

You have found the right page in the Manual.
I personally have not seen one of these in some twenty years... following is my best guess.

On the screen shown on page 146...
Highlight DSP3.

DSP3 is the variable Effect Block, you can choose it as an Insertion Effect (access to a single instrument) or System Effect (access by Send amount parameters from multiple sources from the selected Style).

With DSP3 highlighted, proceed to select an Effect Type, then press the button associated with “Parameters” of that selection.
Here you should be able to select “System” or “Insertion” as the configuration for this processor.

The DSP (3) effect, can be configured for either System or Insertion routing. (This is done from the parameters of the individual effect type;