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.
音箱屬于日本法規的list of category B,是屬于非強制的,可以申請圓形PSE也可以申請S-mark,這個要看你日本當地代理商的要求是什么,一般在日本而言,S-mark的公信力要比圓形PSE有效力,所以建議申請S-mark.而且,如果你的音箱的電源是內置的才可以申請圓形PSE,如果電源外置的話是不允許打上圓形PSE的標志的,只能打S-mark.