How to succesfully replace Opel/Vauxhall factory radio or why your new radio can't pick up much

Opel/Vauxhall calls its factory radios CDxx where xx is a number, in my case it's Opel CD30, originally produced by blaupunkt. CD30 does not play MP3s so I decided to fit new radio - Blaupunkt Melbourne 120. I removed factory fitted CD30, mounted plastic shelf to fit regular ISO sized radio and tried to connect ISO connectors, unfortunately it is impossible because CD30 radio has got it's own standard - to have it done neat and nice I bought adapter for this and used to connect speakers and power supply.
CD30 has got FAKRA connector for antena so I have bought FAKRA to ISO adapter and was naive enough to believe that it is everything what I need.
Radio played mp3 but it picked up only two stations on FM band. After short research I found out information that CD30 radio provides DC component to its antenna connector and this DC component is used to supply antenna preamplifier which is located on the roof right under mentioned antenna. FM preamplifier has to be used because there is not that efficient antenna (it is quite short) and quite long coaxial cable which introduces loses. My brand new fancy Blaupunkt Melbourne 120 is not able to provide DC component so I had to exchange regular FAKRA to ISO antenna adapter to adapter with a circuit similar to this(it is circuit diagram from http://www.electroschematics.com/488/fm-antenna-amplifier/):