was at the CES electronics show over the weekend and saw a few new products that will help with this situation. i also ran the isimple in my car (2002 camaro) and was disgusted wit hte quality rf noise all the time and loading time was terrible. i then swiched to another company that doesent make one for the mustang at all but for me works great has an ipod cable and an aux so i have my xm receiver and my ipod hooked up. it works great never looked back quality is superb. now i just got my gf (2005 mustang 4.0) a sat radio and began looking for a product. thankfully the ces had a few.
the first being PIE. www.pie.net not a bad product but can only run one input
the second is a company Parrot. nice product you canuse bluetooth as well but need to add a small screen. not what i wanted
the third is by AXXESS part number XIA-D01 cool product again alothough can get pricy. this product hasent released yet. they figure within the next few weeks. it allows you to add whatever you want as many inputs as you want even bluetooth. the only problem is for each accessory you need to add a new hub and that can get pricey when each hub is over 100 bucks and bulky for hiding under the dash etc.
the last and my favorite is from Pac audio www.Pac-audio.com their product with the purchase of the cables sold separately will allow you to hook up 2 sources to the radio. in my case her ipod and xm radio. part #aPAC-frd24. charges the ipod and all. i saw it working at the show on a shaker 500 all you have to do is shut one off to use the other. i loved it and recommend it highly. my only problem has been finding a retailer to purchase it from. hope this helps.