XM radio question

Hello all,

A colleage of mine bought XM radio for his parents, and is having difficulties connecting it to their stereo. Since I do not utilize this service, I thought I would ask for input here.

Below is his message, in which I replied. I expained to him about the cartridge preamp issues incorporated in his parent's stereo when connected to the phono inputs (Voltage vs Impedence), specifying what caused the distortion and volume problems when connected there. What is puzzling to me though is why it did not work at all when connected to the other available inputs. Perhaps someone can help. Here's his message:

I recently purchased an XM radio reciever for my folks. They are using an older model (20 year old) stereo that is in very good condition. Anyway... we seem to have an impedence mismatch that is causing occasional "pops and crackles" while listening. We currently have the radio plugged into the unused turntable input. There are also two available cassette deck inputs. The signal from the xm radio is very strong, meaning that we must set the volume on the stereo to the bare minimum to keep it from becoming overwhelmed. The other inputs (cassette) don't even detect the signal from the XM radio... From what i've been able to find online it seems that others are experiencing the same thing and almost universally do not recommend using the phono inputs due to very large impedence mismatches. I've tried the XM radio on my modern digital stereo receiver, and it works perfectly. I was wondering if an easy to use impedence matching device could fix this problem? The inputs to the stereo from the XM radio are RCA jacks... thanks

Well there you have it. Any ideas or suggestions?

Thanks in advance.