The variable attenuator sold by SP (and radio shack) is the biggest POS ever created. It has absolutely no business being in any signal path and SP should be ashamed they even carry that piece of garbage.
Go with a fixed attenuation cable made from quality components. I don't have personal experience with any MM products, but their product, as pictured, is exactly how it should be done with all resistors stuffed into the stereo mini connectors. I've made a few of these before; it's a tight fit and not easily done DIY, so well worth the $30 they are asking.