The stock HU has the Sirius tuner built in. If you remove it, then you remove the tuner. You can use the stock antenna for the aftermarket unit.
I highly recommend installing this gizmo for your aftermarket receiver: http://www.crutchfield.com/p_607SCVD...t.html?tp=6953
It lets you use a dock and play radio but hide it away in the glove box and use the controls on the aftermarket deck. This allows you to have the clean install but the versatility of moving the Sirius tunes to a boombox or home kit.
2002 F-150 XLT Sport
4.6L Triton V8, 3.55LS, Tow Package, Power Moonroof, SVT LED 3-rd Brake Light,
Keyless Door Handle Mod., Autolamp Mod., BedRug, Signal Mirrors (a la Lariat),
ARE LS II Bed Cover