That's an old school box, one of the first designs. In order to use that box with one of today's antennas, you're going to need an adapter if I remember correctly. It steps down the two plug system on your box to mate to a single plug of today's antennas. I'm not sure if you can find it anymore.... Why did you go with this box rather than a modern solution?
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2003 GTI 1.8T
Kenwood LZ800 & Nav/Addzest DRX-9255/MB Quart QSD 3-way/Autotek 5.1 Amp/Illusion Audio ND-10
OEM HIDs/Shaved Hood & Bumper/FK Badgeless Grille/18" BBS RC/APR 91 Chip/APR Turboback/Samco DV/H&R Premium Coilovers/Carbonio CAI/Samco Hoses/PowerSlot Slotted Rotors/Goodridge Stainless Lines
http://www.cardomain.com/id/veedubb8