Sony Xa 300 Auxiliary Input Adapter for Unilink

I purchased a very nice, brand new Sony head unit (in-dash stereo CDXF7710-7715X) from a yard sale that also allowed for XM radio input.  I got the XM universal tuner (Audiovox XMD1000) and the Sony digital adapter (Terk XMDSON100) and had everything running great.  But, I also have a nice MP3 player that I wanted to listen to while in the car.  The Sony head unit only allows XM radio OR auxiliary input.  After doing some research online, I discovered that it "might" be possible to add the Sony XA-300 to allow for an Aux/MP3 addition.  But, I couldn't find anything that told me that "Yes, you can use the XA-300 to control your XM radio".  I finally decided to bite-the-bullet and give it a try.  I won an Ebay auction for $67 (plus $10 s/h) and received my XA-300 in the mail.  I hooked it up to my head unit, plugged in my XM adapter, and added my MP3 plugin.  It works perfectly.My XM radio is still controlled through my XM Source selection from the head unit.  I still maintain full control over channels, searches, displays, and everything.  I access my MP3 player by selecting the CD source and changing the mode to CD3/Aux2.  This lets me plug in my MP3 player and listen to it without any static, distortion, or fade out like an FM modulator causes.The XA-300 only has one unilink controller input and one unilink controller output, so I would not be able to hook up my XM radio adapters and a CD changer to this unit.  It only allows for one or the other.  But, my head unit plays MP3 CDs, and since I convert all my CDs to MP3s, I just burn all the MP3s onto a CD and have no use for a CD changer.It still seems crazy to me to spend this much money just to add an auxiliary input, but at least now I have a head unit that I like that will do everything I want it to.