Round PSE mark for sure. As your product shall apply for Category B products: such as Electronic musical instruments, Radio receivers, Tape recorders, Record players, Juke boxes, and other audio equipment, Video tape recorders...etc.
音箱属于日本法规的list of category B,是属于非强制的,可以申请圆形PSE也可以申请S-mark,这个要看你日本当地代理商的要求是什么,一般在日本而言,S-mark的公信力要比圆形PSE有效力,所以建议申请S-mark.而且,如果你的音箱的电源是内置的才可以申请圆形PSE,如果电源外置的话是不允许打上圆形PSE的标志的,只能打S-mark.