The NX8E is the alarm panel itself. If you have an NX-6 or NX-4, then are limited to only 16 total zones or as I found out, really only 8 the hardwired zone expansion modules can only start at zone 9 and higher. So on my NX-6V2, I had zones 1 through 6 on the alarm panel itself and then the NX216E I bought, I could only use 8 of the 16 ports. So if you don't have an NX8, NX8v2 or NX8E today, now would be the time to upgrade.
NX148E - This is just an LCD keypad
NX1448E - This is just an LCD keypad and can support up to 192 zones
NX216E - This is a 16 zone expansion module. This has extra dip switches that can alter the starting zone numbers; 6 switches compared to 4 on the NX216
NX216 - 16 zone expansion module
NX320 - That is the remote power supply
NX586 - This is a serial to bus to configure the panel using either the DL900 or DLX900 software.
The difference between he NX216 and NX216E is the number of dip switches. The NX216 has four and can operate at zones starting at 9, 17, 25, 33 and 41. The NX8 and NX8v2 didn't support 192 zones that the NX8E supports. So the NX216 modules can be used but can't go higher than zone 48. The NX216E has a total of six dip switches and can go up to zone 192. That is the difference. So nothing wrong with the NX216, they just need to be the first modules to be used if you ever planned on going past zone 48. So if you needed 64 zones, you could use the NX216 from zones 8 to 48 and then you would need to use the NX216E for zones 49 to 64. When I bought my expansion modules, even though I don't plan on having more than 48 zones, I went with the NX216E anyway.
The NX320 vs NX320E is similar to the above. Each module needs to have its own address, the NX320 has four possible addresses, the NX320E has eight. So if you're just going to use a single bus extender, then the NX320 could work just fine. Keep in mind that unless you have an NX-8E, some the extra addresses are not available anyway. So an NX-8 or NX-8V2 could only support four NX-320 remote power supplies even if the NX-320E was used. The NX-320E would need to be configured to only use the addresses supported by the alarm panel. The NX-8E has four additional addresses for a total of eight NX-320E boards. You could use four NX-320 and use the lower address space and then four NX-320E using the upper address ranges. NX320 supports 84, 85, 86 and 87. The NX320E supports 84, 85, 86, 87, 88, 89, 90 and 91.
So the NX320 you can only add four. I went with the NX-320E but there really wasn't a reason I had to since I'll have just the one. The description of the NX320 is a bit different from the NX320E. The NX320 is called a remote power supply and the NX320E is a bus extender that also has a power supply. from the manual for the NX320 it has the same terminals. So it can work as a bus extender, they just renamed the NX320E to have bus extender in its name.
The non E modules are usually less expensive than the E modules. The NX-8E has more memory for the address space, so the modules would conversely need more memory. The sad thing is, memory is cheap but not when the boards were engineered. So if you were never going to use more than 48 zones, the NX320 is a viable option. I just decided to stick with the E modules for future proof but this decision was made before the notice from UTC (Interlogix) about sunsetting the line.