Home Sharing is Missing on iOS 8.4
Apple removed one major iOS feature from iOS 8.4 and you'll need to wait a few months until you can use it again if you upgrade to iOS 8.4 on the iPhone 6 Plus.
Home Sharing allows users to stream music from a computer to the iPhone or iPad on the same network, on iOS 8.3 and below. Apple pulled this from iOS 8.4 and with no iOS 8.3 downgrade users who rely on this should not upgrade at this time.
Apple did confirm that the company is working to add Home Sharing to iOS 9, but that will not arrive until the fall. iPhone 6 Plus owners can still use Home Sharing for videos, just not mu