How can I best use the two TS9 connectors on the back of the M1 to access multiple towers?

Thank you for the answer!

I suspected much of what you have said.  I did not know that CA was one tower only; I thought it could be spread across towers, but, then it made more sense to me to be to only one tower based on the readings.

My current 2x2 MIMO setup is pointing two 11dbi LPD antennas at the closest tower.  I get the following speedtest results: 5Mbps/20Mbps/60Mbps (min/avg/max).  These values match to the LTE signal strength/thoughput charts I have found for my reported signal strength (-100dBm).  These speedtest values fluctuate during the day, and I think they are more dependent on the tower conditions than on my setup.  Adding a signal booster doesn't seem to help much (I have tried it) as my RSRQ and SNR values drop low when its included.  I seem to get the best performance on low power signals with higher quality metrics.

All of which means I am probably already in the optimal configuration.

Thanks so much for your answer!  Please do reply back if you find out anything else.