I would recommend getting the PL and SM talking first. That is pretty simple.
Have you installed the PL yet? That install is quite simple. Read the direction that came with it, if you do not have them, you can get them from the FTS site. Remember to get some goo-gone before starting the install to remove the protectant from the edge connector of the ECM. Do the necessary modifications to the kick panel and have the SM interface cable running out the panel and ready to find a location to install the interface board. I located mine on the passenger side of the ash tray bracing. Easy access for installation of wires for accessories...
Then perform the SM chip change. Very straight forward in the directions. The white wire that was connected to the ALDL port is now taken from the SCM port on the interface board of the PL system. WAAABAAAM, you are done.
Install the software per the directions, and open the program. Start the car and attempt to connect and monitor with the F8 key. You will probably not have connectivity, and will need to "right click" on my computer (not my computer - I am far away from you - LOL...), and select "properties". then select the "hardware" tab and then click the "device manager" button. Yo will need to look at the "Ports (COM & LPT)" section to see which com port the PL system is using to set your software up for communications.
The next thing you know, you will be monitoring the cars system. You can then start adding your additional monitoring systems. I am not familiar with the PLX system - I have an LC1. But I am sure someone will be able to help out here...
Mike