Right up front I'd better let you know you'll have to open the Environment to do this. Techie awkwardness ahoy! Apple haven't yet fully integrated AU3 functionality into Logic 10.4.5 but what's there now is very useful if you don't mind doing a tiny bit of tech admin in the Environment. Still want to boldly go? Really, it's not that bad so let's go.
First thing to know: in LPX 10.4.5 we can now use Software Instrument tracks to provide access to more than one port in each instance of VEP7, with the added performance advantage of highly robust AU3 end-to-end communications integrity, rather than the older port-addressing technique used in VSL's pre-AU3 multiport workaround. (Note that VSL used the word "workaround" with good reason; it wasn't offered as a full production-standard solution. It was a good workaround while waiting for AU3 but it's open to certain highly technical questions which simply don't arise for AU3. So please don't go bashing VSL).
AU3 port assignment is not currently available in Logic's MIDI instrument tracks but it does appear possible to construct multi-port operation using MIDI Standard Instruments and Multi-Instruments, each connected in the Environment directly to a Software Instrument object that is assigned to a VEP7-AU3 Port; I'll cover that in another post, after some more experiments and testing.
We use only one Logic Software Instrument per VEP7/AU3 instance. This acts as the VEP client software instrument device in Logic for all ports and channels in an entire VEP server instance. All the additional tracks created after the first one (up to 768 tracks in total, but currently only 127 MIDI channels max) that are to connect to one VEP instance are merely hidden copies of the client software instrument track strip device in which you have a VEP/AU3 plugin inserted, except that each copy has its own port and channel assignments. Currently, any MIDI FX or MIDI scripts you plug in to the VEP client software instrument will affect outgoing MIDI streams on all ports identically. You won't see any of these instrument copies in the mixer pane of Logic's Main window, but they'll all be there in the Environment's Mixer Layer. More on that in a moment.
The Procedure
1. Launch the VEP7 server. Starting with a completely empty Logic project, create the first software instrument and insert a VEP7/AU3 plugin. You should now be able to see MIDI channel (default "All") and Port (default "1") assignments in the Track Inspector of Logic's Main window. Connect the plugin to an instance of the server.
2. Let's set up 16 single-channel tracks for Port 1. Set MIDI Channel to 1 in the Track Inspector. With Instr 1 track in the track list selected, hit [Ctrl]+[Return] or top-bar menu item Track/Other/New Track With Next Channel, 15 times. Stack these tracks in a folder if you wish. Now you have 16 tracks on one port, each on its own channel.
No need to agonise over the choice between omni (MIDI Channel: All) or single channel tracks at this stage - the steps below will enable you to manage your options later. You can at any future time add more tracks to a port without necessarily having to delete or change anything already done. This ability to layer many tracks in a single port is useful for assigning several omni tracks to one multitimbral Kontakt player in VEP, thereby allowing you to choose an instrument in Kontakt simply by assigning note channel numbers in the score. It's especially handy for changing between tutti and two divisi parts in one staff.
3. Next comes the tricky part: how to create more tracks and assign them to other VEP ports. Having tried lots of other ways, I've settled on this one cuz it works cleanly and predictably.
Create an empty new software instrument (i.e. with no VEP or any other plugin). Now open an Environment window and select the Mixer Layer. You'll see 16 track strip objects representing the 16 tracks you created in step 2, along with the new Instr 2 you've just created, plus some default strips belonging to the mixer. Might be a good idea to tidy it up a bit before you go further - it can get messy.
Select Software Instrument 2 that you've just created and look in the Object Inspector panel. It won't show any Port assignment yet. In the "Channel" assignment field (second one down in the Inspector list) open the popup menu and select "Inst 1". You now have another track connected to the VEP plugin in the first software instrument you created at the top of step 1. Software Instrument 2 has gone. Next down in the Object Inspector list, set "MIDI Channel" to 1 (or leave it at "All" for an omni track) and "Port" to 2.
Hop back to Logic's Main window and satisfy yourself that this new track in the track list is now assigned to Instrument 1, Channel 1, Port 2. You can now use the process in step 2 above to add more channels to this port.
If you created an omni track you'll then need to repeat step 3 if you want to layer more tracks (single channel or omni) into the same port. Also, if during step 2 you happen to try and add another track when all 16 channels are already assigned to the port (by an omni track, for example), then Logic will automatically create a new software instrument which is separate from the VEP client instrument; in this case you can easily re-assign the new track back to the VEP client instrument and a port that you want, as described above in this step.
4. And that's it, basically. For each new port you want to assign new tracks to, or in order to layer more tracks into a port that already has 16 channels assigned, create another new empty Software Instrument then hop into the Environment and re-assign this new instrument to the software instrument that already has the targeted VEP instance plugged in.