After taking out an (unneeded) aftermarket amplifier from my 06 Impreza WRX, I've not been able to find any radio channels. The audio system is all Kenwood, head unit, underseat subwoofer and front & rear door speakers. 

The static coming from the radio isn't changed when the antenna input is plugged into the head unit or taken out. I'm not that clued up about radios so I'm wondering where the issue is?

Has a fuse gone somewhere? Does any part of the antenna need to be replaced? Music comes out perfectly fine when using CDs or Bluetooth. Any ideas? 

 The old radio works perfectly, do I need a a signal amplifier?

Tried out an amplifier and the signal is alot stronger but still not perfect. BBC radio 1, 2 and 3 can be found through auto tuning, other channels can be manually found but the quality is not great. 

Does the antenna itself need replacing?

Did you already rescan it?

I'm wondering if the cars inbuilt antenna needs power sent down the coax to work ( many have inbuilt signal amplifier )

And what you changed // removed it.. ?