You're in a tough spot. If you had access to the roof, I'd recommend a large Yagi such as a Winegard HD7698P. The signal levels looking north are too low to expect an indoor antenna to receive enough power to give you reliable reception.
Amplifiers need a usable signal from an antenna... otherwise, why would anyone bother building an antenna? An antenna is a bit like a microphone, you would not expect to set up a microphone in your apartment, hook it to an amplifier and then listen to a conversation between two people in the park several blocks away. If you turned up the gain, you would hear more noise, but probably little if any of the distant voices.
At football games you occasionally see someone standing on the sidelines with a dish reflector that has an attached microphone. The dish increases the sensitivity of the microphone in one direction so it can 'hear' sound across the field with less interference from other sounds from the back and sides. Small indoor antennas don't have much if any ability to focus their sensitivity. Larger antennas have reflector and/or director elements that focus the sensitivity in one direction, making them able to gather more signal when aimed at a signal source.
The reason you don't see published gain figures for indoor antennas is that generally the have little if any gain compared to a reference dipole antenna. The manufacturer probably thinks that advertising a gain figure in the range of -3 to +3 dB would not help sales, so they just don't say anything about gain.
TinLee.com offers commercial quality single channel filters.
http://www.tinlee.com/MATV-Bandstops.php?active=3#CR7 That you're seeing WTIU suggests that the amplifier in the SS-3000 is not overloading. I doubt that addition of an expensive filter will solve your problem by itself. You need a large high gain antenna mounted outside in the clear, a low noise preamp and possibly, a CH-14 blocking filter.
