Welcome to the forum, cflannagan:
The problem is the wrong antenna.
You need an antenna for VHF and UHF. None of the antennas you list are very good for VHF, in spite of what the marketing description says.
It is the REAL channel number that determines what antenna is needed, not the VIRTUAL channel number.
VHF-Low: real channels 2-6
VHF-High: real channels 7-13
UHF: real channels 14-51
The Omni antenna is not suitable for you. It works poorly in all directions, and its amp doesn't make up for its inherently poor performance.
You don't need an Omni antenna because your desired channels are all in the same direction.
The HDB4X and HDB8X are primarily UHF antennas, but they don't do very well for VHF.
You can add a VHF antenna to your HDB4X or replace it with a Winegard HD7694P.
I doubt that you will need a preamp if you have the correct antenna aimed at 122 degrees magnetic, unless there are trees or other buildings in the signal path.
If the antenna is outside, the coax shield should be grounded with a grounding block that is connected to the house electrical system ground with 10 gauge copper wire for electrical safety and to reject interference. For further compliance with the electrical code (NEC), the mast should also be grounded in a similar manner to drain any buildup of static charge, but the system will not survive a direct strike.
Try it first without extending the mast to see how it does.
How long is the coax to the TV and how many TVs are you feeding?
If your TV has a signal strength indicator, it will tell you how weak a signal can be before you lose it.