Because of reactance, the actual amount of current going to the tweeters at those high frequencies would be but a fraction of the total amount of power output to the speaker system (woofer + tweeter). For this reason, unless your boombox is capable of 40wpc output or more, I'd venture to guess that those 5w tweeters will be fine power wise. As to whether or not they sound as good as the originals, come 'on, how could any of us tell you that based solely on a photo of the tweeters, only your ears can tell you that, although I suspect based on your post that aesthetics are probably very important to you and you'd have to weigh the balance between aesthetics and sound quality.