[GroundUrMast]

The least expensive option at this point is to test reception outdoors using the existing antenna. You attic is one of the impediments to reliable reception. Trees are the next and possibly more significant, especially on wet windy days.

The CS-4 could not do any better with real channels 2 through 13 because these channels are not in the UHF band. You have only one element related to VHF reception, the VHF dipole on the CS-2V or CS-4V. And the dipole is not nearly long enough to offer much Low-VHF (real CH-2 through CH-6) capability.

If I was in the same location, starting from scratch, I'd focus first on outdoor mounting options that avoided the obstruction of trees. That could mean a significant investment in a tower or the services of an arborist/timber cutter. With an unobstructed line toward the transmitters, I could consider a mid sized all-channel antenna like the Antennacraft HD850, or a combination of antennas with similar performance that covers real channels 2 through 51.

If I could not get over or past the trees, I'd step up to a larger antenna combination, for example; An Antennas Direct DB8E to cover the UHF band and allow for flexible aiming. An Antennacraft Y10713 to provide reception of the High-VHF band (real CH-7 through CH-13). And finally, an Antennacraft Y526 dedicated to real CH-5.

Combining two or three antennas that are serving separate bands is fairly inexpensive and easy. UHF/VHF combiners (UVSJ) are available from Antennas Direct, Radio Shack and other suppliers. High/Low Signal Joiners (HLSJ) are available from sources such as 3starinc.com, summitsource.com, solidsignal.com, etc.

You may have noticed that I have not mentioned an amplifier until now... The purpose of an amplifier is to deal with loss in cable and splitters on the output (downstream) side of the amp. Amplifiers may help overcome some noise generated inside your tuner as well. However, no amplifier is capable of 'pulling' signal from the antenna or air. Depending on how long the series of coax is between the antenna and tuner(s) and how much insertion loss due to splitting, an amplifier may be needed. But until your antenna can produce a reliable signal there's no point in talking about a specific amplifier.