| FIrst off, it's more than a part, it has to do with compatibility. The head unit is gonna play a pivotal role in your search for sirius. The oem head unit will have a DIN input for external perephial external components (i.e. CD changer, satelite radio tuner, etc.). It would be up to the dealer to add these perephials. Now if your car was not prewired with a DIN cable steming from the head unit, and most likely terminating in your trunk, I'm sure the dealer probably wouldn't care to install it for you; and that is why they say it can't be done. In that instacne, I would recomend ordering these parts from the dealer, and finding a reputable mobile audio installer that will gladly install it for you. IF for some reason your head unit is not so equipped (highly unlikely), than unfortunately your SOL.
You are however, merely exploring oem dealer installed options. THere are number of aftermarket companies that offer adaptors to add such devices. Yes, it may take a few months before they offer such components for your specific car (it is quite new). Such companies as BlitzSafe and Icelink offer various adaptors allowing Bimmer owners to interface a number of technologies with the oem HU. As long as your oem HU has some type of input (most likely a DIN style), you should be able to find what you need to add Sirius.
Keep in mind you can purchase aftermarket Sirius "add on" tuners from your local electronic retailer, but keep in mind these are usually messy and lack the sound qualtiy that the direct connect pieces exhibit.
BTW, If that '04 6er is yours, I'd love to see some pics. Feel free to throw some up in the showroom. I've seen quite a few cabs out there, but the only HT I've seen was in the showroom floor at the stealership.
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