I was skeptical, but I succesfully installed the GM dual lead XM antenna adapter to the factory XM antenna in my 2003 GMC Yukon Denali, and it works perfectly. There seems to be no degradation of signal quality either. I bought the adapter for www.tss-radio.com. note: I installed the XM tuner, not the sirius tuner. Per TSS, there Kay be signal loss using an XM antenna for Sirius signal reception.
One tip, gently push the plug into the tuner, and be sure that it is fully inserted. I realized my connection to the XM tuner was not made when I powered up the radio for the first time. I had to