While online and offline posted price channels have been well explored, research in B2B multichannel systems is still lagging behind. In this study, we investigate buyers' strategic behaviors in a unique system where an online posted price channel is introduced to the century-old Dutch auction market in a sequential way. We explore the determinants of buyers' choices and their bidding behaviors. We incorporate learning and experiences and unveil how buyers' behaviors may evolve over time. We further examine the conditions under which buyers may split their demand and utilize multichannel strategy. By analyzing an extensive dataset of over 1 million observations, our results highlight the importance of experiences, buyer's demand and product diversity in shaping key decisions. Further, we provide evidence of an emerging group of buyers that complement both the posted price and the auctions channels.