Please define what DBS service is in use.
And which dish / lnb combo you have.
DirecTV uses some 22khz switching, in some cases.
Dish uses some diseqc switching, in some cases.
So, without knowing more, it is impossible to recommend an electronic switch.
The use of an A/B switch is ... an invitation to problems.
For normal operation, both Dish and DirecTV receivers expect to be connected 100% of the time to their dish.
The best and most reliable answer, with the least chance for trouble, is another coax, in my opinion.