So u kno the blue cable thats loose on the aerial part, is that what u connected the amp wire to? I can see a "p. ant" wire on the main loom, u need to attach that to the aerial adaptor, this gives the signal booster thats built into that adaptor its power which will give u the signal strength u need for good reception. The original stereo has one built into the unit, every aftermarket unit i've installed has needed adaptors.
As for the issue with the amp, if this is the exact lead u got with ur stereo as pictured then it has no connections for the amplifier built in. If u look at the original block there will be two slots at the top with one or two blocks slotted in. e.g. the blue and green pictured here
These are where the connections need to be made for the amp. This lead basically bypasses the need for a harness adaptor. Normally u got from quadlock to iso to manufacturer loom. This goes straight from quadlock to manufacturer so u can't adapt it in the same way.
All is not lost however, i'd defo advise u get someone to do this for u, but u could buy a high to low level RCA convertor and convert all ur high level rear speaker outputs (green, green/black, purple, purple/black) to low level rca outputs, create a new remote for the amp, and u shud be able to do it that way. Saying that, i installed a similar unit to this a few weeks back in an x5, and one not long ago in a focus and both had an adaptor with the RCA inputs that could be plugged in if needed. U could use that instead if u have it