Need some help with multiplexing 4 pins into 2

I've done some playing with all the ideas people have thrown at me (and I appreciate all the help given)

I decided to go for the encoder design as I felt it had more stability than the other options since the voltage from the rx module isn't always stable (it caries between 4.6v-5.2v) depending on fluctuations from the supply voltage.

I'm having a bit of trouble hooking the 6 inputs to the 74HC148 and the problem is that the RX module outputs a positive 5V! whereas the inputs of the 74HC148 are active lows and need to be grounded to activate!
That means the only way I can think of having each channel of the rx module activate one of the inputs on the encoder is to have a transistor that pulls to ground for each channel, whenever it's activated... This seems like a lot of extra componentry, so I started looking for a 8 to 3 encoder with more suitable inputs, but I haven't had much luck!

Can anybody recommend an encoder that can take either 5v or logic level inputs instead of active lows? Or possibly even active highs?
Or has someone got a good idea of how I can better work the inputs into the encoder?

Thanks guys!