I have the Scosche #IPFMRDS adapter--hooks in-line with your antenna. Sounds great!
I have mine mounted in the glove box with the plug mounted in a cut-out in my console for a stealthy install. IIRC it was about $150 from Crutchfield.
MikeR

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SOLD---'04 Ranger XLT SuperCab 4x4--4.0 SOHC-Auto--Loaded--Black w/Grey Leather Sport Buckets--Expo OHC--AHI Carbon Fiber-look Trim--Pioneer 290W Sound System--4.10 L/S--Cranked "1" Codes--1" Body Lift--265/75R16 REVO2s--16"x8" Mickey Thompson Classic Lock Wheels with Blue Trim Rings--Bassani Lightning-style CatBack--aFe Intake--Herculiner--Extang FullTilt Tonneau--Black Headlights & Corners--Billet Grille Insert in FX4 Grille Surround--Tinted '06 Tails
New Ride: 2014 Focus ST