7i92 firmware editing

I loaded everything up on a linux VM and it appears to have worked. The file I am looking for is that "seveni92t.hex.bin" correct?

Yes, that's the .bin file that mesaflash expects

Its possible that it would work on Windows directly with some changes in the
xml project file

Just want to make sure that I have this right. Does the first attached image (26pin header.png) match the pin layout on the 7i92t? Or does the second (alternative 26pin.png)?

Some of the pinout files show both HDR26 and DB25 pinouts:

                                                                                      --     P2  26 HDR    DB25            
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 0    PIN 1        PIN 1
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 1   PIN 2        PIN 14
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 2   PIN 3        PIN 2
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 3    PIN 4        PIN 15
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 4    PIN 5        PIN 3
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 5    PIN 6        PIN 16
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 6    PIN 7        PIN 4
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 7    PIN 8        PIN 17
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 8    PIN 9        PIN 5
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 9    PIN 11    PIN 6
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 10  PIN 13    PIN 7
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 11  PIN 15    PIN 8
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 12  PIN 17    PIN 9
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 13  PIN 19    PIN 10
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 14  PIN 21    PIN 11
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 15    PIN 23    PIN 12
        IOPortTag & x"00" & NullTag & x"00",                    -- I/O 16    PIN 25    PIN 13

That is the DB25 pinout listing shows the DB25 pins when connected to a
flat cable terminated at one end with a HDR26 and the other with a DB25

If I wanted to add a smart serial port, how many pins do I need? In some configurations I see that I need 4 (7i76) and in others I only see three (7i96S). I assume I would just need to replace one of the nulltag lines in the module section with one of the sserialtag lines copied from another config and then map the pins I want to use.

You can have as few as 2 wires for a sserial port (RX and TX)

The 7I76 has 4 wires because it has 2 channels:
RX0,TX0 for the on card field I/O and RX1,TX1 for
the external serial expansion port

The 7I96S has three wires because it includes TXEN for RS-485
(say modbus) applications. (sserial does not use TXEN)

So I could just use 2 pins if I wanted to have a 7i84 connected via sserial? That would be pretty slick. For wiring it would just be TX, RX and GND? Though, looking at the 7i84 docs it looks like it needs 2 channels? I do have a 7i96S with a 7i84 in another machine so I guess it does work with just one channel. How would the wiring work?

The remote (Cat5 cable connected) sserial devices need a RS-422 interface
so that just 2 pis at the FPGA level but 6 pins at the interface level

5V
TX+
TX-
RX+
RX-
GND

(The 5V power runs the isolated RS422 interface on the 7I84 etc)

A "local" sserial interface like the field I/O on a 7I76 is just 2 TTL level signals

So are tx- and rx- just GND? So if I were to wire up a 7i84 via Cat5 cable to the 7i92 it would be like this:
OW to 7i92 TX pin
GW to 7i92 RX pin
BL to GND
BLW to GND
BRW to +5v
BR to +5v

Forgive me if this seems like a very simple question, my electronics knowledge, especially serial related stuff, is pretty limited.

No, they are differential signals for noise immunity
That is when TX+ is driven towards 5V, TX- is driven
towards ground and vice versa.

The receive end looks at the difference between RX+ and RX-
signals so any noise that's common to both wires of the RX
pair is rejected.

Typically a RS422 transceiver chip like a SP491 is used for the
conversion of the single ended signals to differential signals.