Been a while, but it's that time...I'm ready to get rid of DirectTV all together, I've already bought a Roku for HuluPlus and Netflicks, and now all I need is antenna signals for my other three TVs.

My preferred option would be to attached a cable from the antenna to the existing 4-way splitter (where the DirectTV cable is connected to), so I wouldn't have to run any cable. I'm hoping someone can help me with this.

Right now, I have a 25' cable from the antenna to a tv that works really well.
I'm thinking about adding a 2-way splitter at the antenna (in the attic), with a 40-50 cable to the 4-way splitter outside the house. I'll only use three cables out that 4-way, the longest being about 70', the second being 60' and the third one being about 30'.

Will the 3412 distribution amplifier be enough, or is there another option in equipment/layout?

Would really appreciate any help.

Well, you can always use the rule of thumb values for loss for a given splitter, length of run, etc. Then you can subtract all of that from your signal and figure if it's enough. Or you just hook it up and see how it goes. Nothing compares to the real deal.

What I'd suggest is that if you have a given reception on a single set, make note of signal strength on some of your channels - maybe best, middle, worst....or all if you like. Signal strength is usually on the TV's diagnostic menu; either bars, % or something. (At worst, you watch the channels after the fact and look for breakup.) Then do your hook up w/all four and see how the original TV fares. If you lose channels or signals are much weaker, then putting an amp inline probably brings it back for you. If all is well, then you may not need it...but I suspect you will. As said before, put an amp near the antenna for best performance; as near as possible means you strengthen good signal vs strengthen a weak signal. Same reason we put microphones as close to a sound source to amplify as clearly as possible.

If you didn't have an amp of some sort already, I think several posts here have made some good recommendations.

Okay, so after a day of sweating up in the attic, I finally got the system to work.

I hooked the antenna to a HDA200 24db distribution amp, which connects to the inserter (came with amp) 25" away, then used a 2' cable to a 2-way splitter (Eagle Aspin 5-1000mhz), from there one cable is 50' for one TV and the other goes 50' to a 4-way splitter (also Eagle Aspin 5-1000mhz, the existing cable/satellite 4-way splitter didn't work well at all), from here the rest of the existing four cables are attached... they're 70', 60', 40' and 30'.

The only problem I had was hand-tightening the connectors, they became loose as soon as I set the cable down (stiffness of the cable rotating them loose), it took me a long while to finally realize the problem and that I needed to use a wrench to ensure they stayed tightened, otherwise, no signal and a lot of head scratching.

Many thanks to all the great guys in this forum that have helped me along the way.