Hi DL DTX is not recommeded on BCCH TRX because this TRX continuously transmits BCCH-signalling info also including SDCCH info.
If you go through Hyper frames and superframes-you will find that BCCH Tsl0 uses 51TDMA frame info in single burst.
Calculate the Time period required to transmit this long burst and You will find that the this time is longer than the DTX interval(480ms).So if DTX is enabled on BCCH TRX,signalling itself get lost,then how the network will work????