Seems to be some confusion here. Are you sure it was Slingplayer telling you to use component cables ? In most cases it is the cable/satellite box after they have implemented HDCP?
What is an 'old' Slingbox 500 ? As far as I know all Slingbox 500s have an HDMI slot. Do you actually have an earlier Slingbox model (Solo, Pro-HD....)
What is happening with your iPhone when you connect ?
What are you trying to control ? Is it the Slingbox or the cable/satellite box ?
What make and model is the cable/satellite box ?
Does it work with the PC ?
Sorry about all the questions but you just haven't given us enough information to help you.