FM and DAB are quite resiliant - You may find simply splitting the cable with a standard Y splitter is enough if your aerial is already recieving a good strong signal.  (50% to each tuner).  If your tuners have seperate FM and DAB inputs you would essentially only get 25% to each input, but again, if your aerial is positioned well, this would more than likely be ok.  The best thing to do is to try it!

If you find you need to boost the signal, most TV dist-amps have an FM input, and than these will boost and distribute the FM signal too, either on their own or with the UHF TV signal too.