Sorry, was busy and not monitoring the new threads here for the last week. Welcome to MAHO E series retrofit.
From your questions, you are rediscovering a number of the issues I also had. Drop me a PM on Practical Machinist forum, with your email address, and I will send you the collected knowledge of "how to retrofit a MAHO" I put together while doing mine. It it pretty well structured, and should help you work through it systematically, so you dont have to reinvent this wheel. I have snap shots of the wiring changes I made in that manual. Not sure if yours will be identical though, that is were you really need a set of wiring diagrams to do such a retrofit. I screwed up the ribbon cable wiring from the 28A1 relay board to the 7i84 the first time I did it as well.
I few things from your posts so far:
1/ Contact DMG and get the wiring diagrams for your machine if you dont already have them.
2/ While you can power the 7i77's 5V from the 5i25, once you add the encoders, you are likely to exceed the Mesa's allowed current draw. I recommend you add a separate 5V din rail mount PSU to power the 7i77 and adjust the jumpers accordingly.
3/ If you are going to do a control panel (rather than just have a PC, monitor and Keyboard laying around), I would recommend adding a 7i73 to interface the control panel. I didn't do that, and needed a lot of discrete wiring, which a 7i73 would have replaced by a single ethernet cable.
4/ Since you will then have 2 ethernet cable daughter boards (7i73 and 7i84, you could consider adding a 7i74 to simply the connection, or make up one of Peter's interface boards:
5/ Make up one of Peters pendants. I did my own before he posted this, and am still not finished with it.
The polarity of the +/-10V analog Servo control is not important. You can switch the behaviour by adding minus in the INI file. I'll download and post my current config files this evening. If you wire it that same as mine, you won't need to use PNCConf, but you will need to compile the Gearbox.comp into your linuxcnc build before it will work.
Mark