Retrofitting a TOS FNG 32 NC

See if there are any Mesa 7i97, that is all you might need.
And if you do need more IO, a Mesa 7i84 will add 32 inputs and 16 outputs, can be placed anywhere as it connects with a single UTP cable to Mesa 7i97 ... i think !
I know 7i77 has an sserial port, 7i76 and 7i76E also have 1, 7i95 has 2 as i have one on the table, so i will conclude the 7i97 has at least 1!

I was looking at the 7i97 first and I like it but it only has 8 outputs, not sure that is enough .
Or is there some advantage to the 7i97 compared to the 7i77?
Price is very similar

The parallel cable and connectors are a bit clumsy, and the cable length is limited. Ethernet should give you galvanic isolation between control computer and machine cabinet which I consider a big plus. Also you have a wider choice of computers using Ethernet since 5i25/6i25 requires a PCI or a PCIe slot, respectively. So you can't use a small ("mini/micro") desktop computer with them.

On the other hand it seems Ethernet is a little bit more finicky to get working well - parallel seems to "just work" while there are some people that seem to have to tweak Ethernet driver and/or PLL settings to get things working (and obviously you need to configure the IP settings on the host). If you want to run your servo loop at faster than normal speed then parallel is probably the way to go - I believe Ethernet is closer to its limits at 1 kHz servo loop? Also Ethernet takes up the Ethernet port of the computer so you need either a motherboard with multiple Ethernet ports, WiFi, or to use an USB-to-Ethernet dongle for the network connection to the outside world (the Mesa card should run on its own net unconnected to anything else).

Overall, unless I had some special requirements, and everything else being equal, I would choose Ethernet over parallel. If you know from the start that you need >6 outputs (note 6 plus drive enables, not however perhaps the 7i77 is better. Then again, as tommylight says, there are expansion cards. In the end, both options should work.

If you can get the 7i92M (notice the M) that would be best as it does not need a clunky cable, it just plugs directly to 7i77.

I was looking to buy a 7i92M just a few weeks ago (for use with a 7i77 that I aldready have) and asked Mesa about availability. There won't be any regular 7i92M's anytime soon since the required chips have a lead time of more than 1 year apparently, but they have a variant on its way: a 7i92TM. Peter said it was "probably 8 weeks or more" away though (this was end of june).

I ended up getting a 7i96S and will use it to hook up my 7i77 via IDC-to-parallel flat cable. A bit more expensive and takes up a bit more space, but it does result in an Ethernet-connected 7i77!

Edit: *And* it gives me lots of GPIO, both isolated (7i96S) and not. Plus an analog isolated pot type output in case I want to hook up a VFD some time in the future. Plus several stepgens if I ever need to use a stepper motor. Pretty nice combo for maximum flexibility!

Based on availability it doesnt seem that there are many options available. 

I would go for a 7i77 and a 7i94 from Mesa. Both are available. 

6 encoder input interfaces is going to be used for x y z spindle and mpg. Leaves one spare for a 4th axis later on....

that should have enougj io for your machine. 
i would be tempted to add a 7i70 for additional io to use for the panel buttons. It looks like your machine use standard buttons for jogging, cycle start etc. You can wirr thr overrides to the 7i70 as well. Mount it in the oparators panel