There is the FM modulator kit available. CircuitCity may be a place to find it if BestBuy doesn't sell it and you do not want to buy it from Crutchfield.
But for the question asked about how you would get this to work if you only have a CD player on your head unit... If your Head unit has auxillary inputs on it or in the back of it you could hook it up that way.
Or you buy this FM modulator kit and hook it up to your new XM radio. Then you simply tune your head unit's radio to a station that the FM modulator tells you to use.
FM modulators in general work very well. I am not sure if you can hook up a regular FM modulator not made for this unit to it or not, but if you can, then you will be able to pick up a cheaper one.
But for the question asked about how you would get this to work if you only have a CD player on your head unit... If your Head unit has auxillary inputs on it or in the back of it you could hook it up that way.
Or you buy this FM modulator kit and hook it up to your new XM radio. Then you simply tune your head unit's radio to a station that the FM modulator tells you to use.
FM modulators in general work very well. I am not sure if you can hook up a regular FM modulator not made for this unit to it or not, but if you can, then you will be able to pick up a cheaper one.