[noggin]

the Problem is that the pi is not fast enough intern to do booth. I use a second pi only as a tvheadend and samba server.

 I've had no major issues with a Pi 3B+ working as both a TV Headend back-end and front-end on the same box for DVB-T/T2 (including DVB-T2 5.1 AAC - not AC3 - audio)  I don't use it for simultaneous streaming to other clients however.  

(The new Pi Foundation DVB-T/T2 uHAT also removes the DVB transport stream data from the USB bus (it uses SPI connectivity over GPIO pins) which potentially reduces USB bandwidth.)