Amplifiers or splitters with amplifiers can help for analog channels, but make it worse for digital channels. On digital, all you care is having a high enough signal to noise ratio. The digital channel tuner will need a certain minimum signal to noise ratio to display fine without pixelation or macroblocking.
Each amp you add amplifies the signal (along with the noise that is already part of this signal) and at the same time adds more noise which in the end decreases you signal to noise ratio. The amp noise figure should be in the specs of your amp. You'll notice that preamp will usually have a very low noise figure compared to a distribution amp. In your case, I'd keep the preamp but remove all other amps if it works without them.
Last edited by stampeder; 2010-06-24 at 05:59 PM.