any sonic changes due to a series configuration of two identicalt speakers will be minimal as Larry pointed out. I would be more concerned with factors of using two speakers in such close proximity not desigend for this purpose such as comb filtering and lobing. Even with this said, the biggest consideration will be how your reciever is going to handle it. Keep in mind that all of the channels in the front shuold be at a relatively similar level. This might present a problem at higher listening levels if the center component demands more power