Why are you using a demultiplexer to drive outputs like this in the first place. It is not the wisest of things to do. By doing this it means you have to have the overhead of multiplexing the outputs if you want more than one to appear on at any one time. There are other output latch chips that will make your design so much simpler, like a 74HC259. Or even a shift register 74HC595.
Why on Earth would this not be wise? Its a signal directing device that operates as I need it to. From what I can tell, the 74HC259 in demux mode does the same thing as what I am doing with the 74HC4051. The reason I am using the 74HC4051 in the first place is because I already had one. We seem to be getting a little off topic here and Im sure there are other ways to do this. Maybe it would be beneficial to include my entire system schematic to illustrate what I am doing and why.
I have a SlingBox that I use to get my HD cable TV service to my cabin over the internet, where TV services are limited but decent speed DSL is available (go figure). At home, where the Slingbox resides, I have 4 DVR units that I wanted to have access too. I have a nice IR controlled component video and audio switch that I use to direct the desired audio/video feed to the Slingbox. I have programmed it to recognize signals from the slingbox and can remotely control the switch to change the video feed. The issue was that if I had the IR blasters going to all the DVR's in parallel, I would be controlling the DVR I was using AND all the other DVR's at the same time (which my roomates might not be happy about). So I needed to develop a way of being able to also switch between IR blasters, based on what DVR I was using at any given time. Here is my system:
The top part includes the DVR's and the IR controlled component A/V switch going to the Slingbox. Below that is my design to decode the IR from the slingbox and relay control signals to individual DVR's. The arduino decodes the IR signals and if it is a signal to change the input on the component switch, is selects the appropriate channel on the Demux so that the IR control signals can be reproduced using the 555 timer and send to only that DVR. The timer is configured in astable mode to produce a 38Khz signal when IR is detected by the IR receiver. Because the IR diodes I am using need to be high power (for the range I need) I need to supply them their nominal forward current of 100mA. This is why the transistors (MPQ2222) are needed as HC devices can only source/sink 25mA.
To repeat, I have bread boarded this, and everything works just as expected. The bi-directional mux/demux sends the 38Khz signals to the appropriate DVR's allowing me to control only one at a time (the one im viewing). I was just concerned with the robustness of using a single current limiting resister for the transistor bases at the input of the analog mux.