Hi Nate,
If you are not yet quite fully submerged with good ideas and things to check....when you have the groundstation setup ready to track satellites you could easily verify how well it can hear by checking signals from any of these cubesats which are presently providing continous beacons in morse code.
I checked them all yesterday and even on a very simple, non directional "whip" antenna the signals from each of them were all easily detectable - without any preamp in front of the IC910 (but with better coax than you have!)
Their designations and frequencies ( +/- upto 9kHz of doppler) are below:
CO 55 Cute 1 - 436.8375 MHz CW going strong - almost 5 years old CO56 Cute 1.7 - 437.3850 MHz Continuous carrier - makes a nice beacon CO 57 Xi-IV - 436.8475 MHz CW going strong - CO 58 Xi-V - 437.4650 MHz CW going strong - approx 2.5 years old - was deployed from SSETI Express
With your directional CP antennas (with the preamp up the mast) and the tracking/rotator configuration working well - you should receive really strong signals from these satellites - even though their output power is around 60mW only.
As you may be aware we are waiting for another launch next Monday so after then there should be even more signals to listen for!
good luck
73 Graham G3VZV