When I made my whiskely ale a few batches ago,I soaked 5 jiggers of Beam's Black in 4oz of nedium toast French oak chips while my dark ale recipe fermented. I put them in a plastic container with a tight lid on it in the fridge during fermentation.
When it was time for secondary,I poured them through a hop sock into secondary. Tied the bag of chips off,& droped them in,racking the beer on top of them. I let it go for 8 days,as the sample was very prominent with oak & bourbon flavor.
In retrospect,when I do it again,I think 3oz of oak with 3 jiggers of bourbon would be better. It'd allow the malts to shine through more with dark ales of lighter malt constituency. In other words,better balance.