Sourdough / Poolish / Biga question

I have a sourdough starter I've been feeding and nurturing for about a year and have used it in breads and pizzas mostly backing out flour and water and inserting amounts of starter.  

I've come to a rustic Italian bread that calls for a Biga.  I figure I could use my starter, even though this Biga is technically a less firm structure.  It has occurred to me to refresh the starter, for this recipe, with a % of WW and Cornmeal to incorporate those flours into the bread and more water than usual to bring it closer to the Biga.

My dumb question is, how should I use my starter to replace this version of Biga in the recipe? If so, how?
Or should I add the starter into the final recipe and mix the Biga as stated and lose the yeast? OR??

Biga
227 g.            Water 
¼-tsp.            Instant Yeast
  72 g.              All Purpose Flour 
  81 g.              Whole Wheat Flour
  41 g.              Cornmeal 

Final Dough
421 g.             Biga 
227 g.             Water  
    3 g.             Instant Yeast
490 g.             All Purpose Flour 
  16 g.             Sea Salt 

I would appreciate and opinions on this.
Thanks
Art