I'm an installer who's still learning the characteristics of digital reception. I bought a HD-7696P and installed it on a roof for a customer. The house has 6 outlets. I'm using a 3 way splitter with the 3.5db leg feeding a 4 way splitter. I aligned the antenna with a DigiAir Signal Meter. I have decent signal at the antenna but need to make up for the losses at the headend. Some of the house tv's get channel 6 and some don't. There is about 30 ft of RG6 from the antenna to the splitters.

Do I need an amp? A preamp? Reconfigure my headend? Do amps and preamps affect the digital signal any differently than the analog signal?

You definitely need to amplify your signal to make it stronger. The difference between a distribution amplifier and a preamplifier is that preamplifier is a 2 part unit with the amplifier mounted at the antenna and the power supply mounted in the house. The preamplifier is used to overcome long downlead cable lengths (losses) between the antenna and your TV set or splitter system.

If you have a good signal at the splitter but not after splitting then you can use a distribution amplifier at this point to build up the signal so that you will have enough signals to overcome splitter loss and cable loss from that point. Winegard’s distribution amplifiers would be the model HDA-100 15dB gain or the HDA-200 24 dB gain.

In your case you have -3.5dB loss at the first splitter and -8.0dB loss for the 4 way splitter so that give you a total splitter loss of 11.5 dB and your 30 feet of cable loss. I would suggest that you use a HDA-100 distribution amplifier ahead of your splitters.